Hi there, a few snapshots of an unprobable voyage with our FlightGear Space Transportation System (STS).
How far the Shuttle can go? But more relevant, from how far can we come back?
I am a newbie to FG, just landed a couple of months ago here because you people just created the perfect simulation for one of my childhood dream, the Space Shuttle. I was 6 years old when it flew, and I still remember watching the news about it. My nickname here is a good summary to what happens when I am in command, so don't be surprised of what follows
Lunch from Kennedy Space Center, with a very special Shuttle. Two of our best engineers have fitted in the payload bay the "Thorsten & Wlbraag" OMS payload kit: an extra reserve of fuel for the Orbital Maneuvering System (OMS, the two hydrazine engines at the back pods of the Shuttle). We also have a scientific payload to explore the inner Van Allen belt, a region where ionized particles get trapped in between 600 and 4000 miles. This is where we go today!
But we want to go back too, so we've started with an inclination a bit higher than the latitude of KSC, at about 39 degrees. You'll see why that's important later on.
Ignition, and leaving home:
Our first challenge is to reach straight a high elliptical orbit, with an apoapsis at 800 miles, full power on the Main Propulsion System (MPS, the three eco-friendly monster engines at the back, they produce water!). Full power means we force the Throttle to the ABORT rating of 109%
Main engines off, external tank separated, fuel dumped done, where are we? As planned, although we're far from any reasonable settings: altitude at apoapsis 810 miles!!! Not so incredible though, the automatic lunch guidance system is actually made by the very same Thorsten: in the FG Space Shuttle, we're in good company, even far from the allowed.
But that is only halfway to our mission. Let's burn almost all the OMS 2 pods reserve, and kick the Shuttle again by a velocity change of 800 ft/s. Why not all? The small amount remaining will be kept from going back...
In the picture below, CUR means our current orbit, TGT means what we're targeting:
Burn ON, and ON for long. Here we go reaching Spain, with OMS engines vomiting their toxic yellow flames (these are all but eco-nice):
Till extinction at an altitude of 380 miles. Very long burn, we've reached an orbit not exactly as planned HA=1372, HP=104, but that's even better, the periapsis at 104 miles means that we will not re-entering the atmosphere, perfect.
Now, we can relax. We still have the full OMS payload kit to burn to increase again the apoapsis. But the burn should be done at periapsis, in a bit less than a full orbit. We deal with all the thermal management issues of the Shuttle, in summary we switch on a lot of heaters and cooler to avoid various lines freezing and various hot stuff burning!
And then, let's kick the Shuttle again by a velocity change of 500 ft/s, burn on again all over the Atlantic, here leaving the East Coast
Done, this time, almost as planned. Current orbit reaches an apoapsis higher than 1800 miles, we'll be exploring the MEO zone, within the inner Van Allen belt.
Ten hours of flight, time to release the payload, above South America. This Van Allen probe actually looks like exactly as the SPARTAN-201 satellite, but that's really a Van Allen probe
Takes some time to use the arm, but here we go, attached and released into Space:
That's about how far we are (finally got my screensaver snapshot!!!).
And now, the big problem... How do we go back with almost no fuel?
Hitting the atmosphere at Mach 29, with the same parameters as for the normal flights produce fireworks. We have too much speed! Thanks to GinGin, this is what the Shuttle is capable of at re-entry, not too much:
Solution: atmospheric braking, we do not attempt of full re-entry, but only bounce on top of the atmosphere to loose a bit of energy, within the thermal limit of the Shuttle.
How to get this? Tune the orbit such that the flightpath angle at re-entry remains lower than the ones in the above picture. With some basic orbital mechanics, that you can get here:
reentry.py
we find that getting a safe flightpath angle of about 2.4 degrees can be obtained if, starting from our current orbit HA=1800 HP=100, we lower the HP at about 44 miles. This needs a small amount of fuel, less than the remaining 20% of the tank reserve. And that's what we get at re-entry, we pass over Earth and rise again to a new orbit (see the Shuttle symbols on the screen, far above the nominal trajectory)
The new orbit had HA=1114, HP=42. The process made us loose 700 miles of altitude at apoapsis, good job! The new orbit is again fine with thermal limit, so we wait again one more orbit to gentle bounce on the atmosphere. In between, we deal again with thermal management, cool the freon by opening the payload door, close them before re-entry...
And we repeat the process, here 3 times to land on HA=344 HP=31, which is now more or less ok to attempt a full reentry.
In the following picture, we're making some small adjustments to rise the periapsis to 35 miles with the RCS thrusters.
The reason being that we cannot choose the point at which we enter the atmosphere, we enter at periapsis. Therefore, we have to plan, three/four orbits in advance, where the periapsis will be, and it should be at about a few thousand miles from our landing site! That's one of the reason the have a inclination slightly larger than the latitude of the departure site, to also allow landing at the departure site.
Here, KSC was quite far, more than 4500 miles, so I chose the White Sands Space Harbor lake bed, but it was quite far too from the expected re-entry point, so we rise the orbit a bit to HP=35 miles. Once we sure, we finally make all the nominal re-entry procedure, fuel dump, and we go deep into the flames:
HP at 35 miles was still a bit low, we lack some energy to reach White Sands, but, again the autopilot will do its best to get that energy back in the following minutes:
Plasma trails and glows:
West Coast in sight:
and we're getting our energy back (the shuttle symbol gets closer to the nominal green curve)
and now, the auto-pilot can work on targeting the landing site
Almost nominal now:
Last turns before the HAC (Heading Alignment Cone) that puts the Shuttle straight in front of the landing lane!
Back on perfect:
Passing down the sound barrier:
And into the heading cone, manual control:
We target the lake bed:
Last moments, virtual lane appears on the HUD, we're a bit low on energy but no worry, and it's a lake:
That's us "alive"
That trip might actually make me the most incompetent flightgear user having flew the highest altitude?
I might also got the highest speed record, MACH 29.2 for the first atmospheric bounce
Hope you'll try the Shuttle too, it rocks!
Cheers,
chris.