Flight Question Interplanetry landing without LEO

[Tommy]

There is an annotated flight recording and notes for performing an inverted re-entry in the XR-2 coming in from Luna available at OH. Search for "Home Direct". This tutorial is also included in IMFD Full Manual/Playbacks (flight #4 IIRC). It is outdated, and was created before the XR Autopilot worked inverted, so it uses manual (COG and elevator trim) controls. but that part can be ignored.

I recommend altering the XR's config to allow bank angles up to 90 degrees (default limits to 60 degrees away from zero or 180) to make the transition from inverted to upright easier - this makes it possible to maintain high AoA throughout the re-entry rather than needing the low AoA during that transition like I did in the tutorial.

If you don't alter the config, when the time comes to roll upright adjust the bank to 120 degrees (or 350, depending), then as the vessel gets close to that set the time accel to .01 while you fiddle with the AP and set it to 60 degrees. The vessel will "buck" a bit during the transition - so make sure the hull temps are well within the green before doing this. Also, your AoA should be quite high (at least 60 degrees) during the transition to reduce the amount of plane change induced.

I've used inverted re-entries from as far out as Saturn - Mars isn't that hard once you get the hang of it. You will need MANY SMALL adjustments while inverted - it is inherently unstable. Watch the VACC closely, and NEVER let it get more than 2 m/s in either direction or you will be in trouble.

 

[RGClark]

Yes, and no.

I would recommend IMFD, which has a great base approach feature to do exactly what you asked. You'll have to learn how to use it though; IMFD is quite complex. However, it may be difficult to impossible set up your approach, depending on your trajectory.
I say yes and no because while you may be able to set up a base approach, a direct entry from interplanetary space will FRY an XR-2. I recommend setting the anticipation angle to 90 degrees and trying an inverted reentry, which is quite challenging!

Another possibility might be to give the craft a waverider shape to get high hypersonic L/D ratio during reentry. It can be in the range of 5 to 8 depending on which model of hypersonic aerodynamics you use:

Waverider Design.
http://www.aerospaceweb.org/design/waverider/waverider.shtml

Compare this to the hypersonic L/D ratio of the space shuttle which is only around 1.
A high hypersonic L/D ratio allows you to stay up higher, longer burning off greater speed before descending into the denser parts of the atmosphere.

Bob Clark

 

[worir1]

thanks for the help

 

[Cras]

Inverted re-entry is not as hard as you think. Once you get a grasp of what you need to do, you will find it very easy actually. I just did one actually with a perigee a bit lower than I would normally like, but it was easy enough to fly out of it and still get the thing slow enough to roll back to heads up and finish up the descent. Actually, in terms of preventing too high a skip on the roll over (which I try to avoid, but sometimes I get a bit sloppy), it was one of my better direct re-entries from the moon.

You can watch all the videos there are, read about it all you like, you gotta do it, and do it often. Practice practice practice, and it will soon become just another thing, nothing too special.

 

[Cairan]

You need a constant high-AOA inverted attitude, but I think I have not seen mentions of doing S-turns to keep a high-AOA constant and modulate the lift to maintain a constant altitude with the S-turns... I've been able to do aerocaptures and aerobrakings pretty much anywhere there's an atmosphere using nothing more than IMFD and Aerobrake MFDs...

 

[Urwumpe]

Compare this to the hypersonic L/D ratio of the space shuttle which is only around 1.
A high hypersonic L/D ratio allows you to stay up higher, longer burning off greater speed before descending into the denser parts of the atmosphere.

Its 1.6 at hypersonic speeds for the Space Shuttle, which is not that bad, considering that it had the design compromise for also landing horizontally on a runway. Buran is slightly better there because it has less drag then the Shuttle, but no significant change there.

The key problem for using a wave-rider shape is, that you can't fly at low supersonic speeds (M<4) with them anymore, the aerodynamic properties quickly detoriate as subsonic flow starts to appear at some spots of their surface. At this point, you need to either stall intentionally (trying controlled flight too long could result in spin) and parachute home or use variable geometry - which is complex and heavy.