Flight Question Direct reentry from moon

[lowerlowerhk]

I am trying to use a XR2 to reenter earth's atmosphere after a journey to moon. I want to do it without burning retrograde and orbit-insertion, ie totally rely on friction to decelerate. I've seen this technique in some videos, but when it is my own turn, i always end up toasted. Is there a procedure for such a flight?

 

[Urwumpe]

No procedure, rather you need to aim for a different reentry window. Since you are faster, you need to be MUCH higher than usual, so the increased heating has no effect.

 

[agentgonzo]

There is a good [ame="http://www.orbithangar.com/searchid.php?ID=3660"]video playback on OH[/ame] that shows you how to do this.

In a direct reentry from the Moon, you'll be doing about 10-11km/s at entry interface. In order to do this without burning up, you need to aim for a perigee of about 68-73km and fly inverted so that the XR2s 'lift' will pull you down towards the earth and prevent you climbing back out of the atmosphere once you pass Perigee.

You can't do this without flying inverted as either you will burn up, or climb back out of the atmosphere having not lost enough speed from your short time aerobraking and then wait until your next orbit (a long time) before braking slightly again and again.

Once your speed is reduced to sub-orbital speeds, flip over so that you are flying heads-up and perform a normal reentry.

Landing at a specific spot is a bit harder as you need to perform your TEI burn so that you hit the atmosphere at the correct position on the correct heading to be able to land at your desired base.

---------- Post added at 13:48 ---------- Previous post was at 13:44 ----------

Also, see this thread

 

[Shadow Addict]

The Home Direct PDF includes a procedure, and I can do it perfectly and reliably each time now.

 

[Tommy]

Just FYI, the "Home Direct" tutorial mentioned by agentgonzo is also included in the IMFD manual, a good reference if you use IMFD for interplanetary, etc.

[ame="http://www.orbithangar.com/searchid.php?ID=4142"]IMFD Full Manual/Playbacks[/ame]

 

[Linguofreak]

Landing at a specific spot is a bit harder as you need to perform your TEI burn so that you hit the atmosphere at the correct position on the correct heading to be able to land at your desired base.

Not really. You're orbit is much more energetic than a circular orbit with the same perigee, and you have wings, so you've got a ton of cross range. I find that on any given approach I can generally be lined up with my target base before I'm down to circular orbital velocity. Then it's just a matter of waiting for your trajectory to become suborbital and skipping out of atmosphere at the right moment that you re-enter again in the vicinity of your target. (I do the double stage reentry to give the heatshield a chance to cool off, even though the XR series doesn't model heat load, only temperature, it gives a feeling of added realism. Plus it gives time to extend the radiator, although I often fly with electronics heating off).

But it's not at all hard to do.

 

[Tommy]

It helps a lot if you are in the ballpark, even with a winged vessel. The technique I used
to time the TIn in Home Direct is rather crude and not exceptionally accurate. You'll notice that after reaching suborbital velocities I have to climb up a bit to extend my range so I can reach the Cape. The Base Approach burn corrects the flightpath so it's over the target, but this could be eliminated (it's really just a plane change made early enough to be reasonably efficient) and Aerodynamic crossrange used instead. An experienced pilot could enter the atmospher just about anywhere at these velocities and still make the target, but it's easier for newer pilots who are still learning the tricks of re-entry to be more or less on course and range at EI

 

[Linguofreak]

It helps a lot if you are in the ballpark, even with a winged vessel. The technique I used
to time the TIn in Home Direct is rather crude and not exceptionally accurate. You'll notice that after reaching suborbital velocities I have to climb up a bit to extend my range so I can reach the Cape.

I count on making a climb after reaching suborbital velocities.

Interplanetary/Translunar reentries generally look something like this for me:

Exoatmospheric approach -> Atmospheric leg #1. Flown heads down. Bank as necessary to line up with target base. -> Transition to sub-orbital regime. Wait until ballistic range (as shown on MapMFD) is less than range to target, then climb to leave atmosphere. -> Suborbital exoatmospheric leg: Coast until second reentry interface. -> Atmospheric leg #2: As traditional reentry -> Approach and landing: As traditional reentry.

 

[Shadow Addict]

I count on making a climb after reaching suborbital velocities.

Interplanetary/Translunar reentries generally look something like this for me:

Exoatmospheric approach -> Atmospheric leg #1. Flown heads down. Bank as necessary to line up with target base. -> Transition to sub-orbital regime. Wait until ballistic range (as shown on MapMFD) is less than range to target, then climb to leave atmosphere. -> Suborbital exoatmospheric leg: Coast until second reentry interface. -> Atmospheric leg #2: As traditional reentry -> Approach and landing: As traditional reentry.

Looks like a good technique, I'm gonna try that.