Scenario Maintaining Shuttle Atlantis in orbit after launch

[richfororbit]

This orbit with the shuttle is certainly my worst. It was terrible, my mistake was point the nose a few degrees while on take off. I usually just go straight up and then do the manuvering.

What I really need is a well explained video tutorial on how to actually get the shuttle into a circular orbit. I really only wanted to use the XR2 for the Martian orbit which was fine. I had the shuttle in mind to do this.

Thank you for the hints and advice.

 

[garyw]

This orbit with the shuttle is certainly my worst. It was terrible, my mistake was point the nose a few degrees while on take off. I usually just go straight up and then do the manuvering.

The shuttle doesn't have sufficent dV to go straight up. On launch the shuttle goes up to get out of the thick atmosphere, very soon after launch it will do a gravity turn, that's why, even before the boosters come off, it's already way off vertical and accelerating.

The key to orbit is acceleration, height is important but you can climb slowly whilst accelerating quickly.

Watch any shuttle launch video. it does NOT go straight up.

 

[Urwumpe]

Look for example here, thats the launch profile of a Proton launcher. While different to a Space Shuttle, it also shows well the principles behind ascent into Orbit:

Of the shuttle, you have to maneuver a bit more radical and thus do a S-shaped trajectory, since it accelerates slower after the SRBs are gone. But the basics are the same. First of all, you try to pitch down as quickly as possible, since you need mostly horizontal velocity. For getting into 150 km altitude, you need just 1800 m/s vertical velocity at the surface. For staying in orbit, you have to accelerate to about 7800 m/s horizontal - notice the difference in magnitude?

Here, I have made a simplified drawing of a Space Shuttle ascent (height had been exagarated for visualization):

 

[Buck Rogers]

The Atlantis demo in Orbiter 100830P1 with the stock Space Shuttle has a LUA Autopilot all the way to orbit, you just have to circularize (NOTE: OMS engines have a 20° offset). If you want to do it manually backstep through the launch, break off the AP and practice, but AFAIK under normal conditions in RL the autopilot is used.

 

[Izack]

AFAIK under normal conditions in RL the autopilot is used.

Indeed, there is no 'manual' mode in a real Shuttle ascent. Everything is very carefully controlled by computers. Reality contains many more challenges in rocketry than what's presented in Orbiter - vehicles really ride a knife edge up into space.

 

[Urwumpe]

Indeed, there is no 'manual' mode in a real Shuttle ascent. Everything is very carefully controlled by computers. Reality contains many more challenges in rocketry than what's presented in Orbiter - vehicles really ride a knife edge up into space.

Thats wrong - you have a the possibility to fly the Shuttle during ascent as commander or pilot. Never without a computer in the loop, turning your inputs into engine deflections. But instead of the software, the human controls the direction of flight.

But AFAIR, no crew has ever flown a Shuttle ascent manually. Even during aborts, you rarely needed to do more than telling the computer to use a different program.

 

[garyw]

But AFAIR, no crew has ever flown a Shuttle ascent manually. Even during aborts, you rarely needed to do more than telling the computer to use a different program.

No ride to orbit has ever been flown on manual, the crews basically ride the rocket up, only on STS-51F did the crew fly an abort and that was an abort ATO. On other flights crews have had to make changes, probably one of the more interesting crew actions was on STS-93 where the crew had to change the engine limits to inhibit, essentially telling the computers to ignore any engine that crossed red line limits and just keep going.

 

[DaveS]

No ride to orbit has ever been flown on manual, the crews basically ride the rocket up, only on STS-51F did the crew fly an abort and that was an abort ATO. On other flights crews have had to make changes, probably one of the more interesting crew actions was on STS-93 where the crew had to change the engine limits to inhibit, essentially telling the computers to ignore any engine that crossed red line limits and just keep going.

Actually, that was STS-51F too. The reason for taking the main engine limits switch to INHIBIT was that the Booster officer in the MCC recognized that the temperature sensors was bad so they would cause a second engine to shut down.

By taking the main engine limits switch to INHIBIT the crew told the GPCs/MECs to ignore any faults/redlines being violated. They would not be automatically shut down.

The only thing that the crew did on STS-93 was take the AC bus sensor switches to OFF to prevent any other shorts from tripping the bus sensors again.

 

[richfororbit]

Okay, I tried this S shape movement in orbit. As the image shows I have done much better than previous three or four attempts. How ever as I have tried I can't increase my orbit path without the external fuel tank attached. I had 13.1 fuel left in it. I suppose my mistake was to jettison it without using it all up.

The craft is at the angle it is because I was attempting to do a prograde without a being at a burn point which is a dangerous step to take.

 

[garyw]

Okay, I tried this S shape movement in orbit. As the image shows I have done much better than previous three or four attempts. How ever as I have tried I can't increase my orbit path without the external fuel tank attached. I had 13.1 fuel left in it. I suppose my mistake was to jettison it without using it all up.

The craft is at the angle it is because I was attempting to do a prograde without a being at a burn point which is a dangerous step to take.

You should always have prop in the ET and jettison, it's normal, that prop is really there as a back up.
The ET gets you suborbital, once there its just a matter of burning prograde at Apoapsis, this is the OMS-2 burn.

 

[Urwumpe]

The thrust vector of the Shuttle is not prograde, but 10.5° away from it. So, you should fly manually and for example keep 10.5° pitch up with wings level and heads up, for accelerating horizontally. Prograde does not work.

 

[garyw]

true but a burn from prograde will work as well

 

[richfororbit]

Well my altitude decreased, so I closed the scenario down. I got a feeling it is the balancing act of doing that S shape and timing when to jettison the tank. If I can succeed at creating an orbit, the OMS burn 1 must be done around the other side of the planet. No burns should be done at all until that point, only thruster use carefully when coasting the planet, if I get that part of this wild ride.

 

[Urwumpe]

Well my altitude decreased, so I closed the scenario down. I got a feeling it is the balancing act of doing that S shape and timing when to jettison the tank.

Altitude may decrease during the burn for some time, that is part of the S-curve.

You go uphill, drop a little and when the centrifugal force approaches the gravity because your horizontal speed increases, you start accelerating upward again.

MECO should happen with PeA at about -50 km and +50 m/s vertical velocity (so Apogee is ahead of you). The OMS has only propellant for about 600 m/s velocity change in the real one, Orbiters Atlantis a tiny bit more, but still not enough for big maneuvering. You should only be barely suborbital (-50 km < PeA < +80 km is OK)

Yes, it is very hard to fly manually, that is why there are simpler vehicle in Orbiter to practise it.

 

[PhantomCruiser]

It's not easy for a novice to fly the stock shuttle manually. You really need to either use the script LUA autopilot (read the manual) to watch it and see what it does and when it does it.

Or, grab the Shuttle Fleet. It's autopilot is pretty sweet, and you can also learn from it (flight performance is more realistic as well). And AutoFCS is great for learning how to re-enter and spot land on the runway. It'll do it itself, all you need to do it watch, and drop the landing gear when the time is right.

Another alternative is the shuttle here is Steve's [ame="http://www.orbithangar.com/searchid.php?ID=5744"]Project-Outposts: Wet Workshops V2.1.0[/ame] as it has a launch autopilot also, but it is a little bit strange when you first use it (does the same job, just in a different manner, can't explain it as it is something you'd have to see). I don't know if AutoFCS works with it or not...

Why use an autopilot you may ask? To the best of my knowledge and belief, Shuttle Commander Joe Engle is the only person to perform a manual reentry during STS-2 (not bad for a rookie).

 

[kamaz]

Hi Rich - let's start with something a bit easier, and then work back to the Shuttle. Jump in a Delta Glider, and default Cape Canaveral scenario, and get it up to orbit. Don't worry about flying through buildings, or no runway ... just full throttle, get airborne, raise gear and you are on your way. The benefit of the Delta Glider is that it has unrealistically (or 'future') powerful engines, so you can concentrate on the Orbit MFD and not worry too much about everything else.

DG may not be a good choice because it takes off horizontally.

OTOH, Themis-A takes off vertically, it has a nice autopilot, and I wrote a step-by-step tutorial for it.

 

[richfororbit]

Fortunately I have managed to get into orbit, unfortunately spent two days, practically my entire mission duration doing prograde, and retro burns at various locations to help create a circular orbit.:dry:

Not sure if should continue with this first flight. I had to edit the fuel at least five or six times.

I suppose the next procedure once I have managed to get into an orbit, even if wonky. Do I open the cargo bay doors? Or was that a step that happens before circular orbit ideally that is?

 

[garyw]

Why do you want a circular orbit?

I tend to go for a 220 x 280km orbit and then chase down the ISS.

Normal shuttle procedure is:

Launch
Film the ET
OMS-2
Open the Cargo Bay Door
Extend the KU antenna

 

[Urwumpe]

Also, remember that the gravity of Moon and sun will also perturb your orbit and make the Orbit MFD display varying data. Find out how much accuracy you really need in which phase of flight, the same is done in real spaceflight. The less accuracy you need, the better for your fuel, since correcting every lunar nano-g is very expensive.

 

[richfororbit]

I suppose being a complete beginner I shouldn't be so serious about it. :dry:

Right, I guess I'll proceed with the doors opening. And then my goal is to launch my satelite. At what altitude should I be launching it, 300Km or well bellow 270KM or 260KM.