Discussion NTR Shuttle

[Eagle1Division]

So, I'm being a bit rash to post this so quickly after I came up with the idea, but It's really neat...

The idea is to replace the 3 SSME's with Nuclear Thermal Rockets. The objective is that this new nuclear shuttle should be able to either go to the Moon or Mars.

To facilitate the lower thrust, and the fact the ET would be heavy through the entire ascent, lowering the shuttle's acceleration even further, either larger (such as the 5-segment) SRB's would be added, or even LRB's to provide a much larger high-thrust boost Delta-Vee.
(Perhaps the first stages of some other rockets?)

I doubt the NTR's will provide enough thrust power for taking off from Mars, and the shuttle's External tank would have to be attached the whole time, so the idea would be to put an excersion and ascent module in the payload bay, along with some packages to extend the shuttle's duration.

Interestingly enough, the Apollo LM would comfortably fit in the shuttle's payload bay with plenty of room to spare.
Apollo LM:
14x13.3x17.9 ft (width x depth x height)
14,696 kg

Payload bay:
15x60 ft (diameter x height)
25,060 kg (May drastically increase with NTR engines)

I've run by the math using different types of propellant, LH2 is too thin, so using the existing ET I got a mass ratio far too small, and Ammonia doesn't have enough Isp, the highest Delta-Vee came from using CH4, Methane.

Liquid Methane is much warmer than LOX, especially LH2, so less insulation would be required, but it's heavier weight means more structure mass. I'll assume the two roughly cancel.
Filling the LOX and LH2 volume of the ET with Methane...
(Discluding SRB's)
Mass Ratio: 7.27
Exhaust Velocity: 6,318 m/s (NTR Solid Ch4)
Delta-Vee: 12,535 m/s

Compare the original Space shuttle (also disculding SRB's)
Mass Ratio: 6.42
Exhaust Velocity: 4,142 m/s (Two-thirds Vacuum ISP over SL ISP)
Delta-Vee: 7,704 m/s

So the NTR design gives an extra 4,830 m/s of Delta-Vee. I'm also planning to use the first stage of some other liquid-fuelled rocket to replace the SRB's, which will add even more Delta-Vee.

That's enough for now, I'll get back to this tomorrow, so here's the work order:

First:
SRB Replacement
Requirements:
~13.5 MN of thrust (I can add more engines to get this)
-Delta-Vee greater than 4,795 m/s (current SRB Delta-Vee)
-Must be an existing rocket first stage.
(I'll try the Falcon 9 and Delta-IV first stages. Those are roughly the same size as the SRB's and are capable of being used as boosters.)

Second:
Possible Mission:
Is a lunar mission possible with this much Delta-Vee? How about a mars mission? A hopeful reminder is that the lander will be in the payload bay, and that a Lunar lander can easily do this with plenty of room and weight to spare. A Mars lander is a different story, though! Can I get a Mars lander to fit in a 15x60 payload bay?...
(Note Mars has 8.7x lunar mass and 2.3x lunar gravity, though, unlike the moon, aerobrake will be possible, very small Delta-Vee needed to land.)

A hopeful reminder is that the figures I worked above - where the shuttle minus the SRB's has 12,535 m/s of Delta-Vee, include a full payload bay. Once the mission is done, the orbiter+ET will be 25 tons lighter, since the lander could be left behind.
(But, if it's possible to bring the inert lander home, then that would be wonderful! Fully Re-usable Mars or Moon mission! How's that!?)


[PS, I intend to make this an add-on, but I've seen similar things titled as discussion. I want some back and forth discussion here, so I'll leave the title as that...]

 

[N_Molson]

I certainly don't want to discourage add-ons developpement, but here are my first thoughts about this :

- While I know there are many shuttle-enthusiaths people around here, I still greatly doubt of the usefulness of sending a lifting body to a planet that has not enough atmosphere to provide lift. Wings, TPS, control surfaces, hydraulics, all this stuff is heavy, and there is no need for it. On the scale of the Shuttle, a TPS able to protect the spacecraft of a reentry from interplanetary velocities would add a lot of mass.

- The Shuttle is powered by 3 fuel cells. Maximum duration : 15-20 days. And you can't turn these on/off like that. Even bringing spares would be a risky operation (you need a lot of heat (power) to power a fuel cell on, and if it fails to ignite... end of the story).

- Re-usability of the lander ? Anyway, any efficient lander design is probably going to have a descent stage and an ascent stage. What you leave on the Moon allows you to lift more payload to say it in a very simple way.

- I don't really get how you are going to land on Mars ? With the Shuttle ? You'll need hover engines and then you have a DG-like thing.

- Replacing SRBs by LOX/LH2 or LOX/Kerosene engines isn't going to help you. SRBs have a small ISP, but the fuel is very "dense" (a small quantity can deliver a lot of thrust during a short time). LOX/LH2 is the contrary (a big quantity can deliver a moderate thrust during a moderate time). LOX/Kero is somewhere between those. See the Energia boosters (LOX/Kero, 4 of them were necessary to do the same work than the 2 SRBs). If you need more power from the SRB, strap 2 additional SRBs. If you need them to burn for a longer time, add segments/change diameter.

(Edit)

- You would need to protect the TPS during a Moon or Mars trip. In space, a grain of dust can do nasty damage, provided it comes from the wrong direction. And we know the TPS is very sensitive to kinetic damage.

 

[T.Neo]

Major problems I see here:

- You can't just drop NTRs into the Orbiter boattail. An NTR will have different structure and volume requirements than the SSME.

- Radiation shielding! Big problem. You'll need tons of radiation shielding between the crew/payload and the engines, or else they'll get fried. This would be something like borated polyethylene, which isn't exactly the densest material around...

- Thermal control. The Shuttle orbiter was built for a LEO thermal environment, not a BEO one. You'd at least have to perform some modifications to the orbiter, but how effective they would be is anyone's guess.

- As N_Molson mentioned, power is a problem. Shuttle fuel cells couldn't be restarted on-orbit. You can extend mission duration with an extra LH2/LOX pack (this existed and was known as the Extended Duration Orbiter pallet, and was lost on Columbia). A pair of solar panels could be deployed from the payload bay, but I'm not sure if you could use electricity from them to restart a shut-down fuel cell. Apparently these fuel cells also needed a certain load- something like at least 30% of their total capacity- fulfilled at any one time, or something bad happens to them.

- Again, taking a shuttle beyond LEO makes no sense. The wings and landing gear and TPS are justifiable as a return system from Earth, but having to lug them all the way elsewhere? It doesn't make sense to me.

- You might have trouble performing TLI, LOI, and TEI with that dV. You would also need restartable engines. The SSMEs weren't restartable, but then again these are not SSMEs...

- Thermal control on the ET. At least Methane is better than LH2 (or even LOX), but in space, especially under harsh solar radiation, it could be a problem.

- Does the orbiter have a TPS capable of withstanding reentry? Even if you can guide it sufficiently for a BEO reentry, won't the TPS overheat and fail?

- 4 830 m/s doesn't create much of an improvement in transit time for a Mars mission. Maybe you could still have a crew living in the middeck for that amount of time, but the orbiter also has little if any radiation shielding.

To read more about some of the problems of an NTR spaceplane, read here. I also ended up using Methane for it's combination of density and performance.

I ended up with 14 000 tons of radiation shielding, and even that probably wasn't enough (though I also had propellant tanks between the crew and engines which would have shielded them somewhat from radiation).

Also of note is the length of the vehicle. There is no aerodynamic reason for this- it is primarily to reduce the radiation exposure on the crew. Radiation exposure goes down with the inverse square law. This results in a vehicle that is very long and narrow compared to STS.

The vehicle would also potentially have the problem of wanting to fly backwards.

Another issue is thrust. NTRs are very low thrust, probably even too low to propel Shuttle stack to orbit. Good luck finding an NTR with enough thrust... that doesn't spew radiation everywhere.

I abandoned the idea because an NTR spaceplane of that sort simply isn't advantageous enough to outweigh the extra cost and problems. At the end of it, I would have needed airbreathing engines to help me get to orbit as well, and by then I was just thinking "Why do I have an atomic, airbreathing spaceplane, when Skylon is just airbreathing and is actually being pursued in reality?"

The best bet would be to have a spaceplane or some other kind of surface-to-orbit shuttle to haul components for an NTR-based BEO architecture instead. This was actually proposed in the very early days of the Shuttle.

- Re-usability of the lander ? Anyway, any efficient lander design is probably going to have a descent stage and an ascent stage. What you leave on the Moon allows you to lift more payload to say it in a very simple way.

What's wrong with a re-usable lander? Everyone goes on about re-usable launch vehicles, and a lunar lander at least doesn't have to endure the same sort of stresses an RLV would.

Also, the most efficient lander design is likely one with only one engine(s), that just leaves its descent tanks and landing gear on the Moon. This way, it doesn't need to carry extra fuel to lug around an engine which is parasitic mass for part of the journey.

- I don't really get how you are going to land on Mars ? With the Shuttle ? You'll need hover engines and then you have a DG-like thing.

Hover engines would probably be the worst thing to put on it...

You could land on Mars if you had very, very big wings, and skids. Unfortunately the problem is that the Shuttle has neither...

- Replacing SRBs by LOX/LH2 or LOX/Kerosene engines isn't going to help you. SRBs have a small ISP, but the fuel is very "dense" (a small quantity can deliver a lot of thrust during a short time). LOX/LH2 is the contrary (a big quantity can deliver a moderate thrust during a moderate time). LOX/Kero is somewhere between those. See the Energia boosters (LOX/Kero, 4 of them were necessary to do the same work than the 2 SRBs). If you need more power from the SRB, strap 2 additional SRBs. If you need them to burn for a longer time, add segments/change diameter.

Density is not mass. You could replace the SRBs with LRBs that could have the same mass and provide more dV. They would just be larger physically- which isn't a problem unless they conflict with stuff in the VAB/on the launch pad/on the stack itself.

Additional segments don't affect burn time, but they do affect thrust (I think). Diameter change would affect burn time.

Filament-wound SRMs were studied for STS. They could have a lighter structure than the normal SRMs, and increase payload. They were also intended for Vandenberg launches to boost payload.

A depiction of an STS stack with LRBs can be found here. The size of the boosters is striking, but not impossible...

- You would need to protect the TPS during a Moon or Mars trip. In space, a grain of dust can do nasty damage, provided it comes from the wrong direction. And we know the TPS is very sensitive to kinetic damage.

Which is more dangerous? A week in LEO, filled with debris, or 6 days in deep space, filled with fewer debris?

 

[Urwumpe]

I would really embrace TNeos expertise there... he literally gave his brain a 100% meltdown trying to engineer such a beast some time ago. And I mean engineering. He really looked for facts instead of just doodling what he wants.

 

[Eagle1Division]

Major problems I see here:

- You can't just drop NTRs into the Orbiter boattail. An NTR will have different structure and volume requirements than the SSME.

It's kind of taken for granted , the structural revisions for NTR...

- Thermal control. The Shuttle orbiter was built for a LEO thermal environment, not a BEO one. You'd at least have to perform some modifications to the orbiter, but how effective they would be is anyone's guess.

How would thermal control be an issue? LEO and BEO are both space, radiators will continue to work the same.

- As N_Molson mentioned, power is a problem. Shuttle fuel cells couldn't be restarted on-orbit. You can extend mission duration with an extra LH2/LOX pack (this existed and was known as the Extended Duration Orbiter pallet, and was lost on Columbia). A pair of solar panels could be deployed from the payload bay, but I'm not sure if you could use electricity from them to restart a shut-down fuel cell. Apparently these fuel cells also needed a certain load- something like at least 30% of their total capacity- fulfilled at any one time, or something bad happens to them.

Wait, I remember reading in the reference manual that two fuel cells are used for launch, then the orbiter switches to two others for on-orbit, then switches back to the first two for re-entry. That's shutting them down and re-starting them. Not all of them at once, but some of them.

- Again, taking a shuttle beyond LEO makes no sense. The wings and landing gear and TPS are justifiable as a return system from Earth, but having to lug them all the way elsewhere? It doesn't make sense to me.

No. It doesn't. I'm not proposing this as a real-life project, just a realistic orbiter mod. I want to take the shuttle places in at least a realistic way XD

- Does the orbiter have a TPS capable of withstanding reentry? Even if you can guide it sufficiently for a BEO reentry, won't the TPS overheat and fail?

It depends on the trajectory, and how much Delta-Vee is available for braking. I've actually done re-entries before without any plasma forming, or getting above ~400 *C. Surely a BEO reentry can be done with a ~2,000 *C roof with the same methodology...

- 4 830 m/s doesn't create much of an improvement in transit time for a Mars mission. Maybe you could still have a crew living in the middeck for that amount of time, but the orbiter also has little if any radiation shielding.

- Thermal control on the ET. At least Methane is better than LH2 (or even LOX), but in space, especially under harsh solar radiation, it could be a problem.

- Radiation shielding! Big problem. You'll need tons of radiation shielding between the crew/payload and the engines, or else they'll get fried. This would be something like borated polyethylene, which isn't exactly the densest material around...

All mass-adding problems...

Another issue is thrust. NTRs are very low thrust, probably even too low to propel Shuttle stack to orbit. Good luck finding an NTR with enough thrust... that doesn't spew radiation everywhere.

I found [ame=http://en.wikipedia.org/wiki/Project_Timberwind]this gold[/ame] on Wiki's NTR page.

Timberwind 75 Specifications:
* Diameter: 5.67 ft (2.03 m)
* Vacuum thrust: 165347 lbf (735.5 kN)
* Sea level thrust: 147160 lbf (654.6 kN)
* Vacuum specific impulse: 1000 s
* Sea level specific impulse: 890 s
* Engine mass: 5500 lb (2500 kg)
* Thrust to Weight Ratio: 30
* Burn time: 357 s
* Propellants: Nuclear/LH2

Atomic Rockets has the old NERVA and NTR projects, Timberwind is more modern, according to the Wikipedia Nuclear Thermal Rocket article, the higher performance comes from modern materials and computer aided design that weren't available for those old nuclear rockets.

I abandoned the idea because an NTR spaceplane of that sort simply isn't advantageous enough to outweigh the extra cost and problems. At the end of it, I would have needed airbreathing engines to help me get to orbit as well, and by then I was just thinking "Why do I have an atomic, airbreathing spaceplane, when Skylon is just airbreathing and is actually being pursued in reality?"

The best bet would be to have a spaceplane or some other kind of surface-to-orbit shuttle to haul components for an NTR-based BEO architecture instead. This was actually proposed in the very early days of the Shuttle.

"It's an incredibly silly sort of ship to design", but that's the type of rocket project Rho has.

What's wrong with a re-usable lander? Everyone goes on about re-usable launch vehicles, and a lunar lander at least doesn't have to endure the same sort of stresses an RLV would.

Also, the most efficient lander design is likely one with only one engine(s), that just leaves its descent tanks and landing gear on the Moon. This way, it doesn't need to carry extra fuel to lug around an engine which is parasitic mass for part of the journey.

I actually was saying how nice it would be to have a reusable lander. It's just taking it back to Earth means more payload mass, which hurts Delta-Vee with our fixed amount of fuel in our ET.

Though I never meant to consider bringing the descent stage back. And a mars craft would only need a heat shield and parachutes for a descent stage, it's descent rockets would be very small with only a tiny Delta-Vee needed to go from parachute speed to landing speed.

Hover engines would probably be the worst thing to put on it...

You could land on Mars if you had very, very big wings, and skids. Unfortunately the problem is that the Shuttle has neither...

We're carrying a lander in the payload bay.

Additional segments don't affect burn time, but they do affect thrust (I think). Diameter change would affect burn time.

Filament-wound SRMs were studied for STS. They could have a lighter structure than the normal SRMs, and increase payload. They were also intended for Vandenberg launches to boost payload.

A depiction of an STS stack with LRBs can be found here. The size of the boosters is striking, but not impossible...

As I'm starting to see, I think the delta-vee of a booster isn't the only factor. Delta-Vee is a product of exhaust velocity and mass ratio. But mass ratio isn't important because we're just throwing away the inert mass once the boosters are done thrusting.

What boosters do is add impulse to the vehicle without costing mass. So a better way to measure a booster would be by it's impulse. This is why the LRB's are so large, they need to be very massive, because
J = m * Dv
J is impulse in Newton-Seconds
M is mass
Dv = Delta-Vee, change in velocity.

The SRB's have a small Delta-Vee, but are very heavy. Today I've gone over using the Delta-IV CBC (First stage/booster) for the nuclear shuttle's boosters.
SRB: 1,632.6975 MNS (MegaNewton Seconds)
CBC: 786.84 MNS
(This was painfully hard to find, info on the first stage alone. Took hours and hours...)

Radiation is certainly an issue, though... Mars is most likely off the list with a Delta-Vee of only an additional 4,830 m/s once in LEO, nevermind radiation and power issues. But that (Delta-Vee) may go up with larger boosters, or even 2 extra. So it's very unlikely, but I wouldn't say no for sure just yet...

Next I think I'll look into using 4x 5-segment SRB's. Extra segments adds more thrust, smaller bore (hole in the propellant, motor, whatever it's called) adds more burn time. Since the shuttle can't withstand 3+ G's, these boosters will need smaller bore, the 2 extra boosters and extra segment will add thrust, mass and Delta-Vee.


Has anyone made a mod where the Saturn-V is modified with an NTR engine on either of the upper stages? That would be a neat Mars mission, and I think IIRC NASA may have actually studied it.

---------- Post added at 10:49 PM ---------- Previous post was at 10:35 PM ----------

I certainly don't want to discourage add-ons developpement, but here are my first thoughts about this :

- While I know there are many shuttle-enthusiaths people around here, I still greatly doubt of the usefulness of sending a lifting body to a planet that has not enough atmosphere to provide lift. Wings, TPS, control surfaces, hydraulics, all this stuff is heavy, and there is no need for it. On the scale of the Shuttle, a TPS able to protect the spacecraft of a reentry from interplanetary velocities would add a lot of mass.

Soft re-entry to keep the temperature down. Shuttle is an aerodynamic vehicle, so it can control it's reentry.
Plot for an extremely shallow re-entry, then turn upside-down at 25* AoA and use lift to keep from glancing off the atmosphere. (Well, not so much glancing off the atmosphere, as much traveling in a straight line while the Earth is curved. Use lift to follow Earth's curve, allows for a very shallow re-entry. Don't actually know if that's shallow enough, though.)

- The Shuttle is powered by 3 fuel cells. Maximum duration : 15-20 days. And you can't turn these on/off like that. Even bringing spares would be a risky operation (you need a lot of heat (power) to power a fuel cell on, and if it fails to ignite... end of the story).

Larger fuel tanks to increase duration?...

- Re-usability of the lander ? Anyway, any efficient lander design is probably going to have a descent stage and an ascent stage. What you leave on the Moon allows you to lift more payload to say it in a very simple way.

I know... But if there's enough Delta-Vee for it, it would be nice to have it be re-usable. The ascent stage, anyways.

- I don't really get how you are going to land on Mars ? With the Shuttle ? You'll need hover engines and then you have a DG-like thing.

Lander in the payload bay. Carries heat shield, parachutes to slow down, and only very low mass ratio retro rockets, just enough to slow down from parachute speed to touchdown speed, probably not enough to warrant another stage.

- Replacing SRBs by LOX/LH2 or LOX/Kerosene engines isn't going to help you. SRBs have a small ISP, but the fuel is very "dense" (a small quantity can deliver a lot of thrust during a short time). LOX/LH2 is the contrary (a big quantity can deliver a moderate thrust during a moderate time). LOX/Kero is somewhere between those. See the Energia boosters (LOX/Kero, 4 of them were necessary to do the same work than the 2 SRBs). If you need more power from the SRB, strap 2 additional SRBs. If you need them to burn for a longer time, add segments/change diameter.

That's probably what I'll end up doing.

- You would need to protect the TPS during a Moon or Mars trip. In space, a grain of dust can do nasty damage, provided it comes from the wrong direction. And we know the TPS is very sensitive to kinetic damage.

Replacement tiles would probably be carried, much better on mass than a shield of some kind.

 

[T.Neo]

It's kind of taken for granted , the structural revisions for NTR...

Of course. The problem is that they wouldn't be trivial.

How would thermal control be an issue? LEO and BEO are both space, radiators will continue to work the same.

In LEO you have the Earth providing some thermal radiation to you, plus the fact that you pass behind the Earth's shadow for 45 minutes every 45 minutes...

Wait, I remember reading in the reference manual that two fuel cells are used for launch, then the orbiter switches to two others for on-orbit, then switches back to the first two for re-entry. That's shutting them down and re-starting them. Not all of them at once, but some of them.

Which reference manual?

No. It doesn't. I'm not proposing this as a real-life project, just a realistic orbiter mod. I want to take the shuttle places in at least a realistic way XD

Er, well, in that case I propose:

Build a super-heavy lift booster similar in size to Nexus.

Mount STS and a full external tank on top of it.

Either try to modify the SSMEs to be air-startable, or devise a way to replace them with something like the J-2X.

Of course, you will have to deal with all the other problems. But I think that technically, it could probably be less challenging. :lol:

It depends on the trajectory, and how much Delta-Vee is available for braking. I've actually done re-entries before without any plasma forming, or getting above ~400 *C. Surely a BEO reentry can be done with a ~2,000 *C roof with the same methodology...

Plasma forming in Orbiter doesn't dictate real heating conditions in reality, as far as I know...

And you can spend time skipping off the atmosphere from orbit, but a BEO reentry is an entirely different thing- for one, you will be coming in at a much higher velocity than from a LEO orbit.

You might need the lift of your vehicle to prevent you from flying off into space again. In other words, you might end up having to fly upside down...

All mass-adding problems...

Of course. And additional mass is a problem.

But it also isn't like adding that mass is easy...

For example, that radiation shielding... probably has nowhere to go in the orbiter vehicle structure.

I found this gold on Wiki's NTR page.

Timberwind 75 Specifications:
* Diameter: 5.67 ft (2.03 m)
* Vacuum thrust: 165347 lbf (735.5 kN)
* Sea level thrust: 147160 lbf (654.6 kN)
* Vacuum specific impulse: 1000 s
* Sea level specific impulse: 890 s
* Engine mass: 5500 lb (2500 kg)
* Thrust to Weight Ratio: 30
* Burn time: 357 s
* Propellants: Nuclear/LH2

Atomic Rockets has the old NERVA and NTR projects, Timberwind is more modern, according to the Wikipedia Nuclear Thermal Rocket article, the higher performance comes from modern materials and computer aided design that weren't available for those old nuclear rockets.

That is still very low. At 104.5% design thrust, the SSME produces nearly 2200 kN...

"It's an incredibly silly sort of ship to design", but that's the type of rocket project Rho has.

And? At least you can use a nuclear rocket in a more sensible manner, if you wish. ROCS was not an optimal concept from a theoretical engineering or financial point of view.

I actually was saying how nice it would be to have a reusable lander. It's just taking it back to Earth means more payload mass, which hurts Delta-Vee with our fixed amount of fuel in our ET.

Though I never meant to consider bringing the descent stage back. And a mars craft would only need a heat shield and parachutes for a descent stage, it's descent rockets would be very small with only a tiny Delta-Vee needed to go from parachute speed to landing speed.

Due to the thin Martian atmosphere, you'd likely need some sort of landing rockets to do some braking, since the atmosphere is not thick enough to rely on aeroshells and parachutes alone.

EDS on Mars with heavy payloads is apparently quite difficult... maybe there could be a solution in some sort of... sky-crane... sort of... thing.

We're carrying a lander in the payload bay.

Assuming a considerably sized Mars lander could fit in the payload bay...

As I'm starting to see, I think the delta-vee of a booster isn't the only factor. Delta-Vee is a product of exhaust velocity and mass ratio. But mass ratio isn't important because we're just throwing away the inert mass once the boosters are done thrusting.

It doesn't matter to the vehicle after booster seperation, but it does matter beforehand...

What boosters do is add impulse to the vehicle without costing mass. So a better way to measure a booster would be by it's impulse. This is why the LRB's are so large, they need to be very massive, because
J = m * Dv
J is impulse in Newton-Seconds
M is mass
Dv = Delta-Vee, change in velocity.

The SRB's have a small Delta-Vee, but are very heavy. Today I've gone over using the Delta-IV CBC (First stage/booster) for the nuclear shuttle's boosters.
SRB: 1,632.6975 MNS (MegaNewton Seconds)
CBC: 786.84 MNS
(This was painfully hard to find, info on the first stage alone. Took hours and hours...)

Delta IV CBCs would likely not provide enough thrust for this vehicle to get off the ground. I tried a Shuttle stack in Velcro Rockets with four Atlas V cores as boosters, and the thing got off the pad... but it was a very slow riser.

You will likely also need more booster thrust, to make up for a lot of the 20% liftoff thrust that the SSMEs provide. Now that you have less thrust from the orbiter, you could also run into structural and stability issues...

Radiation is certainly an issue, though... Mars is most likely off the list with a Delta-Vee of only an additional 4,830 m/s once in LEO, nevermind radiation and power issues. But that (Delta-Vee) may go up with larger boosters, or even 2 extra. So it's very unlikely, but I wouldn't say no for sure just yet...

Next I think I'll look into using 4x 5-segment SRB's. Extra segments adds more thrust, smaller bore (hole in the propellant, motor, whatever it's called) adds more burn time. Since the shuttle can't withstand 3+ G's, these boosters will need smaller bore, the 2 extra boosters and extra segment will add thrust, mass and Delta-Vee.

You can't just add extra boosters to the stack. You get a whole lot of problems, including:

1. Changing the support points for the boosters.

2. Changing the launch pad and stacking operations.

3. Accelerations that could be too high for the vehicle to endure.

4. Aerodynamic forces too high for the vehicle to endure.

5. Vibrations too high for the crew/vehicle to endure.

6. Damage to the FSS/MLP due to extra exhaust plumes.

Has anyone made a mod where the Saturn-V is modified with an NTR engine on either of the upper stages? That would be a neat Mars mission, and I think IIRC NASA may have actually studied it.

NASA did study a "drop in" NTR engine for the S-IVB. A nice quick-and-dirty way to simulate it would be to create a new config file for the S-IVB from Velcro Saturns with the characteristics of the NTR-propelled S-IVB.

EDIT:

Larger fuel tanks to increase duration?...

Not really a new concept (though it involved more tanks, not larger ones). See [ame="http://en.wikipedia.org/wiki/Extended_Duration_Orbiter"]Extended Duration Orbiter[/ame].

There's a limit to how much reactant you can carry, obviously.

I know... But if there's enough Delta-Vee for it, it would be nice to have it be re-usable. The ascent stage, anyways.

There have to be better reasons for reusability than "it's nice to have". Only if it is economic, advantageous, and not adversely impacting on safety, is it a good idea to reuse something.

Replacement tiles would probably be carried, much better on mass than a shield of some kind.

That is a bit of trouble since... every tile on the Shuttle is unique. :blink:

There are ways to repair tiles on-orbit, but they have limits.

 

[Eagle1Division]

Which reference manual?

The Shuttle Reference Manual, I've heard it been called.

Okay, looking back I can't find it, which is odd, because I distinctly remember something 1 and 2 are used during ascent and reentry, and 3 and 4 are used on-orbit.

Er, well, in that case I propose:

Build a super-heavy lift booster similar in size to Nexus.

Mount STS and a full external tank on top of it.

Either try to modify the SSMEs to be air-startable, or devise a way to replace them with something like the J-2X.

Of course, you will have to deal with all the other problems. But I think that technically, it could probably be less challenging. :lol:

Aw, but that takes all the fun out of trying to get it into orbit with engines that produce half the thrust xD

I don't need a full ET. Just enough for a lunar transfer. So far I think Mars may be off the list.

Plasma forming in Orbiter doesn't dictate real heating conditions in reality, as far as I know...

And you can spend time skipping off the atmosphere from orbit, but a BEO reentry is an entirely different thing- for one, you will be coming in at a much higher velocity than from a LEO orbit.

You might need the lift of your vehicle to prevent you from flying off into space again. In other words, you might end up having to fly upside down...

How accurate are the temperature indicators on the DGIV?

Flying upside-down is fine as long as the pitch on my AoA is positive.

For example, that radiation shielding... probably has nowhere to go in the orbiter vehicle structure.

It can take less room... If I use lead.

That is still very low. At 104.5% design thrust, the SSME produces nearly 2200 kN...

Key here is the T/W ratio. I can scale up the engine for more thrust, but T/W ratio is the big thing, and it's 30, where the SSME's have about 70.

EDS on Mars with heavy payloads is apparently quite difficult... maybe there could be a solution in some sort of... sky-crane... sort of... thing.

EDS? ...And I did mention using a retro-rockets to slow from parachute speed to touchdown.

Delta IV CBCs would likely not provide enough thrust for this vehicle to get off the ground. I tried a Shuttle stack in Velcro Rockets with four Atlas V cores as boosters, and the thing got off the pad... but it was a very slow riser.

You will likely also need more booster thrust, to make up for a lot of the 20% liftoff thrust that the SSMEs provide. Now that you have less thrust from the orbiter, you could also run into structural and stability issues...

I added another RS-68 engine to the CBC, gives it the T/W ratio of the SRB's, but to get the total thrust of the SRB's, 4 RS-68's are needed, though that only gives a burn time of 60 seconds.

3. Accelerations that could be too high for the vehicle to endure.

Lower the thrust of the SRB's by decreasing the bore diameter.

The other issues... Not really anything that would involve a mod in Orbiter to address.

 

[T.Neo]

The Shuttle Reference Manual, I've heard it been called.

Okay, looking back I can't find it, which is odd, because I distinctly remember something 1 and 2 are used during ascent and reentry, and 3 and 4 are used on-orbit.

Are you sure you are not maybe remembering something related to the APUs? Those are on during ascent to operate the hydraulics for the SSME engine gimbals, and on again during reentry and landing to operate the control surfaces.

I don't need a full ET. Just enough for a lunar transfer. So far I think Mars may be off the list.

A full ET would allow you to get to Mars and back, wouldn't it?

How accurate are the temperature indicators on the DGIV?

I don't know, but I most certainly wouldn't bet my life on them.

Flying upside-down is fine as long as the pitch on my AoA is positive.

It isn't fine if the temperature of the TPS exceeds its limits...

EDS? ...And I did mention using a retro-rockets to slow from parachute speed to touchdown.

Entry, Descent, and Landing.

The problem of course is that you're not talking little small retro-rockets, but retro-rockets that could be quite large and require quite a large propellant supply.

Lower the thrust of the SRB's by decreasing the bore diameter.

It isn't that simple. For one, you'll reduce dV if you decrease the size of the SRBs. And you could change burn characteristics.

And vibration and sound waves could still be an issue... not to mention the problem of bathing the launch pad in flames.

Or even having an adverse on the vehicle itself... for example you could increase heating of the aft dome on the LH2 tank.

The other issues... Not really anything that would involve a mod in Orbiter to address.

Not being able to fit in enough radiation shielding to prevent your crew from dying horribly is a pretty important detail, generally.

Also there would be other issues- for example, insulation or other modifications to the ET, thermal changes, support for solar power, and whatever external visual changes there would be from trying to shoehorn a couple of NTRs into the rear of the Orbiter...

 

[Urwumpe]

The Shuttle Reference Manual, I've heard it been called.

Okay, looking back I can't find it, which is odd, because I distinctly remember something 1 and 2 are used during ascent and reentry, and 3 and 4 are used on-orbit.

Since the Shuttle has just three fuel cells, this is pretty doubtful to be right.

Also, you will NEVER power a fuel cell down without need, and need means: Not enough power being consumed. Fuel cells work best when having a pretty high load on them, they cool out when not getting enough load and cease working. Also, you often don't even shut them down, but only switch to standby to prevent freezing.

The APUs are powered down completely after reaching orbit, since they have limited fuel and only last about 1.5 hours.

The computers are modified: The backup flight system (GPC5) is completely shutdown, since it has no On-Orbit software, the four GPCs with PASS software are reconfigured, so you have two running GNC software and one running system management, while the fourth is powered down in a freeze-dried state: When you turn it on, it will instantly have GNC software ready and can be included in the redundant set with the other two GNC computers.

Otherwise, you only power off or on groups of subsystems completely. The star trackers are all powered on in Orbit, the rate gyroscopes and the accelerometers are powered down for example (you only need the RGAs and AAAs during reentry, because they have faster update rates as the more precise IMUs). GPS is kept running...but GPS has little impact on the Shuttle anyway.

 

[Capt_hensley]

^ "Re Shuttle manual" there's a two part PDF Shuttle reference manual, I downloaded it, and I have the URL on my other HD(It's a Scanned Printed Manual)

The HSF reference is good, and has up to date(if 2002 is up to date enough for you) info, but the two volume PDF is the old, and strangely, the only printed and official manual. Dated 1988.

I'll dig it up and get back with you, but it should read the same as the HSF web version above.

There's an operations manual that would explain on-orbit Ops and is more up to date


Edit:
"Broken Link Ommitted"

 

[Urwumpe]

Excuse me, but I prefer the primary source.

http://www.nasa.gov/centers/johnson/news/flightdatafiles/index.html

Also, you should really read the files instead of just posting links to them. The SCOM is the primary introductory reference material about the Shuttle and all of the Shuttle operations. Not just orbit ops. And not just going really into the details, you have other books about this, for example the many work books.

The primary source of information for the orbit ops is the Orbit Checklist, the Orbit Pocket Checklist and the mission supplements for it.

 

[Eagle1Division]

This wasn't a very big, or important idea. Other things would make much, much more sense, like an NTR upper-stage Saturn V. If I do make this an addon, it'll be simple and unrealistic

I won't give up on the OTV like this, though. The reason I'm not persuing this is because I want to divert my attention to the OTV and the series of vessels to follow: http://orbiter-forum.com/showthread.php?t=23781

It's much more realistic
And the next ship once the OTV is finished, a massive LOX/LH-2 cislunar people carrier... Well, there's just something awesome about a multi-thousand ton LOX/LH2 vaccuum-only spaceship x)

One Issue I face with both is LH2 leaking...

 

[T.Neo]

It's much more realistic

I would caution against claiming that a concept is realistic. :shifty:

One Issue I face with both is LH2 leaking...

Yeah, that is a problem. What is the rate at which LH2 diffuses through a propellant tank?