Are these all the shuttle has?

[george7378]

Hi all,

I have just launched the 'Carina' satellite into orbit, and want to return to Earth. I have a problem though; the engines on the rear of the shuttle don't give me nearly enough power to retro-grade from 7100 m/s for a re-entry, but they use up all the fuel by about 6700 m/s.

Are these engines all the shuttle has:

If so, I doubt I will make it back. Any tips?

Thanks.

 

[Artlav]

Ever heard about aerobracking re-entry?

 

[ar81]

Tip 1: Spend less fuel during ascent
Tip 2: Maneuver near apoapsis to maximize fuel usage
Tip 3: Avoid orbit alignment maneuvers. They are very fuel expensive.

Space shuttle has a fairly realistic fuel supply and engine power.
So anything you can do to save precious fuel may be useful.

 

[ex-orbinaut]

George,

Are you sure you have the concept of deorbiting right?

What you want to be concentrating on is getting your Pea down into the atmosphere (use the Orbit MFD) and not worrying too much about speed at the precise moment of the deorbit burn.

Read section 16 of the Orbiter.pfd Manual in the Doc folder, for starters.

 

[MJR]

Your speed does not matter for de-orbiting. You need to get your periapsis lowered and the atmopshere will lower you speed.

 

[Artlav]

Hm. Sorry for the first throw.

What is your altitude?
7100 m/s sounds like it's well over 1000 km.
If yes, then the problem is that the shuttle was not designed to return from that far.

 

[MJR]

You should have an orbit of 350x350 for deploying the satellite.

 

[Urwumpe]

You don't need to slow down by more than 150 m/s velocity change with the space shuttle in all thinkable cases, that is about 25% of the fuel on-board.

Slowing down to 6700 m/s, over 800 m/s slower than orbital, looks like you have not understood yet what reentry is. Even from unrealistic 1000 km altitude, you should be able to return without using more than 50% fuel.

 

[MJR]

Ballistic entry that is. Lol.

 

[Urwumpe]

Ballistic entry that is. Lol.

That is not ballistic, that is already targeting for lithobraking. :lol:

 

[MJR]

:rofl:*Stall, Stall, Stall.

I think he probably had unlimited fuel and tried to get the speed to 0 thinking it will make him stop.

 

[RisingFury]

:rofl:*Stall, Stall, Stall.

I think he probably had unlimited fuel and tried to get the speed to 0 thinking it will make him stop.

He wouldn't have made it into orbit with unlimited fuel.

 

[MJR]

Well in orbit you can keep filling it back up.

 

[ex-orbinaut]

Hi, popped in again, and have some second thoughts....

If you want to get into the physics of it, I think the velocity at a given point of the orbit could be used to determine your deorbit parameters. All you are doing at the end of the day is altering your eccentricity by retro burning and turning your current point into (more or less) into the apoapsis with a lower velocity than required for a "perfectly" concentric orbit, for that particular axis.

Surely it would involve delving into Kepler's Second Law; the one about sweeping an arc which defines an area with reference to the focus (Time over Area being the constant). The burning question is; how do you go about calculating the area of a segment from an eccentric focus, so that this Law can be of any use for "leisure" type claculations in Orbiter?

PS:
Okay. Scratch that last question. I have found it....

http://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion

 

[2552]

The real Space Shuttle isn't like the one in Armageddon. Once in orbit and without the external tank, the 3 main engines (SSME's) do not and cannot fire again until returned to Earth and reused. The OMS engines above the SSMEs are what are used for orbital maneuvers and reentry.

 

[ar81]

That is not ballistic, that is already targeting for lithobraking. :lol:

No, no lithobraking.
He seems to be trying to use the shuttle as a lunar lander... on Earth...

 

[george7378]

Hi again,

I have just downloaded (and launched a satellite from) the DGIV from Dan's Orbiter page. I have a question regarding re-entry:

How do I know when to perform the de-orbit retrograde burn? I am just guessing at the moment. Is there an equation?

Thanks.

 

[TMac3000]

Up to a certain point, it's up to you. I wait until I am 135 degrees, or about 15,000 kilometers from my target base (Map MFD will give you this information). The trick is not figuring out when to do your de-orbit burn, but how much of a burn to do.

1. Set your computer on De-orbit Display (Press DISP 2)

2. Use the following formula for your entry angle: arctan(altitude/distance). Burn retro until the predicted angle matches your result. This method usually gets me within 600 km of the Cape.

 

[insanity]

It depends on the orbit you've got, but in a nice 350*350 orbit you should start the burn on the opposite side of the world. When I fly a typical DGIV reentry I set my orbit about 300*300 and base aligned. When the distance to the base reads around 19M and falling I start a retrograde burn by using retro thrusters while my ship points prograde. When I get into discernible atmosphere (200km) I adjust the burn so that at 40 degrees pitch up I fall on top of my target. Aerobrake MFD can be used for helping you set the burns up.

 

[TMac3000]

It depends on the orbit you've got, but in a nice 350*350 orbit you should start the burn on the opposite side of the world.

Also true I usually do my manual check rides at 250x300, but I tried my method from a higher orbit the other day, and missed the Cape by 2400 km But perhaps that was because I kept second guessing my altitude calculations?