X-99 Dual Star

[Eagle1Division]

Hello,

Normally I'm working on one project or another to pass time, in this case, I've ran into a fairly interesting idea...

So the Venture Star was a huge promise and a dream that ultimately failed. There are probably some folks around here that have more information on it than I do (which I would be interested in), but from what I understand the issue was technical problems with the LH2 fuel tank, because it required new materials to reach such a high mass ratio while providing the insulation and pressure containment.

So my idea was to add a booster. Okay, it wouldn't be an SSTO anymore, but:
+ The all-metal heat shield still drastically reduces turnaround time
+ A new liquid booster would have lift surfaces and a light heat shield to allow it to be fully reusable.

~The booster would be in an outline configuration, and sit on top of the Dual Star (over the payload bay, as depicted above), so that it doesn't have a chance of foam-strike on the all-metal heat shield.

+ Because the booster is fully reusable, the entire system still has all the advantages of an SSTO, without facing the issue of large mass ratio or extremes of the acceleration profile. Mating the booster to the vehicle would be trivial in comparison to the Shuttle's procedures.

The advantage of an SSTO is it's 100% reusability. That hasn't gone away. The booster in this case, if designed correctly (very heavily, that is), turnaround operations could be as easy as refilling the tanks, without major engine overhauls every flight. Because it's a booster and not the primary rocket, it can afford to be somewhat heavier, so extra mass, which means not working as near structural limits, means not such strict and comprehensive overhauls and maintenance will be required.

The Booster is a lifting body, it separates at the point where it can glide and land at the MARS (Mid-Atlantic Regional Spaceport) on [ame=http://en.wikipedia.org/wiki/Wallops_Island]Wallops Island[/ame]. This target can be reached after launching from the KSC at 42* inclination with a MECO at around ~2,500 to ~3,000 m/s.

This would restrict the missions to high-inclination orbits, but if a low inclination orbit is required, the booster could carry jet engines for a powered glide to Nova Scotia or a target on the west coast of Africa, depending on the inclination of the mission. This isn't too much of an exotic idea, the Buran spacecraft was designed to use a jet engine assisted glide, and they will only need to thrust the empty booster, which doesn't carry a large heat shield, meaning it would be extremely light.


With an ascent time of ~600 seconds, it would only need a mass ratio of 6 for the central stage. The booster will only need a Delta-Vee

I'll post more as I flesh out the idea more.

Same-day update:

Orbiter:
Delta-Vee: 7,640 m/s
Mass Ratio: 5.6767
ISP: 450 s
LOX/LH-2

Booster:
(Provides avg. 50% thrust)
Delta-Vee: 5,600 m/s
Mass Ratio: 8.275
ISP: 270 s
LOX/RP-1

Boost Delta-Vee: 1,400 m/s
Velocity at separation: 2,800 m/s

[As you'll notice, it's very easy to calculate separation velocity, boost D-v, and total D-v when the thrust is at exactly 1/2 ]

Q's:

Although Linear Aerospike nozzles are supposed to get a better ISP at every altitude, from the data provided, the SSME's actually have a better ISP than the Venture Star's RS2200 Aerospikes:
RS2200: http://www.astronautix.com/engines/rs2200.htm
SSME: http://www.astronautix.com/engines/ssme.htm

According to what I read, the Venture Star wouldn't use hypergolics. So what does it use for RCS then?



PS, if anyone noticed, the picture is of the SSTO from Ace Combat (5?).

---------- Post added at 10:42 PM ---------- Previous post was at 03:01 AM ----------

So, since I'm using the Venture Star as a baseline for the orbiter, and I've drastically reduced the mass ratio, I have 2 choices:

A: Shrink fuel tanks, and decrease overall vessel mass.
(Orbiter Fueled Weight: 260 tons)

B: Expand payload capability, and leave overall mass the same.
(Orbiter Fueled Weight: 991 tons, same as Venture Star)

So far, I'm choosing to go with B. After I calculate the mass of the booster (Which I'm still trying to figure out how that'll work. I think it's tied to the Impulse. J = M * Dv)
, I'll drop the mass if it's too large. But expanding the payload gives a payload mass of ~85 tons, and drastically increases the payload fraction of the vehicle. (Once again, discounting booster, since I don't know it's mass.)

But there's no garuntee the payload fraction will be much better after I add the mass of the booster, but, 85 tons is a very nice number for futuristic heavy hauls. This is a mid-near future vehicle, so 85 tons would be great for assembling space stations, or carrying modules of a Moon or Mars vehicle into orbit for on-orbit assembly. 85 tons could be enough to lift an entire moon mission, though. Or an entire small space station.

Or, most notably of all... A space hotel.

So at the moment I'm going with 85 tons, the heavier configuration. Same wet orbiter mass as Venture Star wet mass, but overall it'll be heavier because of the booster. But even if the mass doubles... That's still 2,000 tons. About the same as the STS. Not too bad.

---------- Post added 08-25-11 at 03:59 AM ---------- Previous post was 08-24-11 at 10:42 PM ----------

I just found out the SSME's are being stored for use on future vehicles as of the end of the shuttle program. Nice, reusable engines... I'm looking at those for the Dual Star. Better performance than the Venture Star's RS2200 Linear Aerospikes, apparently.

(I wonder if the 347s sea level ISP data actually comes from static tests. Because with flowing air it would be much higher, since it's the moving air that acts as a nozzle for Aerospikes. I'll read up on this some more.)

 

[Arthur Dent]

KIsn't the whole Venture Star design based on the Aerospike engines? Wouldn't using the SSME's require a complete redesign of the vehicle?

 

[Eagle1Division]

KIsn't the whole Venture Star design based on the Aerospike engines? Wouldn't using the SSME's require a complete redesign of the vehicle?

I don't really understand why...

According to Encyclopdia Astronautica the SSME's actually have better specific impulse (linked in OP) (but perhaps not during trans-sonic and supersonic atmospheric flight?), I'd like to check this with another source, but it's not too surprising considering the program got cancelled... And I'm changing the mass ratio anyways.

Perhaps because the structure can't take the force of smaller engines (single points of force) instead of an evenly dispersed linear aerospike? Once again, the structure can be greatly reinforced with this drastically lower mass ratio (from ~10 give or take 2, to ~5.7). Maybe i'll pull a few tons from the payload to account for that.


Also, I'm changing the mass ratios, ascent profile/acceleration, and payload mass. Those things are much more major than changing the engine. In essence I am redesigning the vehicle. I'm really using the Venture Star more as a baseline, in terms of non-MPS systems mass, aerodynamic shape offering a high internal volume for propellant, and heat shield. So there's a considerable number of differences.

Most notably is the lack of need for the high-performance composite materials that caused the Venture Star program to fail. In other words, no untested technologies here. Except perhaps for the re-usable, aerodynamic LRB, which, however, is only based on existing aircraft and shuttle technology.

Thanks for the input, much appreciated :thumbup:

---------- Post added at 04:49 AM ---------- Previous post was at 04:37 AM ----------

Okay, I think the way I was calculating the booster design was wrong...

I'll revert back to using Newton-seconds of impulse. That makes the most sense, before I was doing some tricks with the Delta-Vee and such, and the booster mass only came out at ~147 tons.

...Also, ATM I'm only able to calculate the Delta-Vee at which the booster separates. I need to set it to separate at a certain horizontal velocity (2,500 - 3,000 m/s), so I'll have to figure out how to do that (In other words, account for total gravitational loss up to different points during the ascent).

I'm still optimistic. I also just learned about finding tangents using limits in calculus. This could be key to creating that ascent profile I've needed for so long, and finding gravitational drag. In other words, at what delta-vee my horizontal velocity would be 2,500-3,000 m/s. (Create a profile, get the Sin values for vertical, Cos. values for horizontal, or the net values and use summation to find totals, or totals up to a certain point.)

 

[Arthur Dent]

Perhaps because the structure can't take the force of smaller engines (single points of force) instead of an evenly dispersed linear aerospike

That's what I meant. The SSME's seem to be superior on the paper, they are also quite heavy, and require a different mounting and thus a different structure.


The VentureStar had different engines then the Space Shuttle because of its different design approach.
An engine failure of one of the SSME's would be a more (mission) critical thing than an engine failure in the VentureStar.

 

[Eagle1Division]

That's what I meant. The SSME's seem to be superior on the paper, they are also quite heavy, and require a different mounting and thus a different structure.


The VentureStar had different engines then the Space Shuttle because of its different design approach.
An engine failure of one of the SSME's would be a more (mission) critical thing than an engine failure in the VentureStar.

Well, yeah... It'll have a different structure for the engines than the Venture Star, but it's not the Venture Star. I'm using the Venture Star as a baseline, I'm not copying it then modifying it. I guess the name "Dual Star" is kind of misleading, then. It's a whole new vehicle.

That's because there are only 3 SSME's on the shuttle, but 7 RS2200's on the Venture Star, that don't even operate at full thrust. So if an engine fails, an engine on the opposite side would cut off, and the other engines would throttle-up.


Higher thrust means less gravitational drag, which means less delta-vee is required to reach orbit. But no matter how you design a vehicle, in order to have "Press to ATO/MECO" capability (where you can continue to orbit even if an engine fails), then you'll have to have a certain amount of unused/reserve thrust, which means unused/wasted engine mass.

The space shuttle throttles down the engines near MECO to maintain < 3 G's, so it has some reserve thrust. The Venture Star would run the engines at a lower throttle AND cut off 2 of it's 7 engines before MECO, so it has a lot of reserve thrust. Not to mention a single engine failure means losing 1/7th thrust, as opposed to the STS, where a single engine failure means losing 1/3rd thrust.

So really it's a trade-off in-between saving engine mass and having that "Press to MECO" occur earlier in the flight.

Really what I'm saying is that the fact than an engine failure isn't such a big deal on Venture Star has pros and cons. It means it can carry less mass to orbit, but "Press to ATO" and "Press to MECO" happens earlier in the flight, meaning a risky RTLS or TAL abort is less likely to happen. (It may be possible that there was no TAL or RTLS if a single engine failed. I don't know that much about the Venture Star to say, but I think this may be the case.)


If I put 7 engines on a brand new shuttle, and ran them all at a low throttle, let's say 60% of rated thrust, then I'd have a lot of wasted engine mass. I could get the same thrust for 4 engines at 105% rated performance. BUT, 7 engines at 60% would mean there's lots of unused thrust that I can use in case of emergency, which is what they did with the Venture Star.
(Which, IMO, was a horrible idea for an SSTO. You'd want to save every gram, but instead they had a lot of wasted engine mass... Sure it's safer, but ultimately, extra inert mass proved fatal.)



If the structure can take 35 m/s^2, then I can use 4 SSMEs on the Dual Star. "Press to MECO" would happen 33% earlier in the flight than it did for STS, because of the extra engine.

Also, the SSME's already exist and they're sitting mothballed in a hanger somewhere. Figuratively dusting them off and plugging them into the new shuttle is much cheaper and more efficient than designing an entirely new engine system.

If I do choose to use new engines, they'd be linear aerospike engines, and I'd do it so that I can have engines that don't have to be refurbished with every flight. I'd do this by not working so near material limits. Heavier engine, but a much lower cost and shorter turnaround time (which lowers cost again) would be well worth the extra LOX/LH2 and RP-1.

 

[Eagle1Division]

I have bit of a problem right now. That's developing the ascent profile/pitch program for the vessel... This part will take a bit to figure out so sorry if the updates are slow in coming.