Flight Question XR2 energy management questions

[mode1bravo]

After doing some once around the earth reentry practice from KSC
in the XR2 I got it down to where I can usually make it back landing
dead stick like the shuttle,(dumping all main/scram fuel B4 entry)
but my technique could be refined.

Deorbit is done at 18000km range and decreasing from a 225km X
230km orbit with a Perigee of 50km 28.6 Inc. During entry I try to keep V
Descent varying from 75 to 100m/s until around 4.5kps below 50km
alt the speed loss and descent rate really start to pick up to where
you have to stair step decrease pitch (from 40deg) and any bank
angles right before coming out of the entry.

I come out of the entry at around a velocity of 2.8Kps and 45km
alt about east of New Orleans.Cross range of course not being much
of a problem at this inclination at KSC so I'm not concentrating
on banking to correct this much, more to control descent rate.I
start S turns just b4 Florida coast, but it feels like you would
run out of energy if done earlier. Crossing the Florida coast is
at 2.5kps 38km alt.Most of the time I overshoot the cape slightly
but can still make the field carefully doing a wide turn high enough
just flying with trim.

I'm wondering if I got it close and just messing
up the timing and distance of the S turns?

Is this in the ballpark on velocity altitude and range?

I was wondering what the more experienced XR2 pilots here could

offer for improving this?

Nothing like turning on final off the HAC knowing your going to make the field
after returning from space hearing the subsonic boom like dropping out of warp drive...:rofl:

 

[Urwumpe]

I don't really yet ballpark by velocity altitude or range... i just use the deceleration until I am about 150 km away from the base. if you go by 16 m/s² deceleration, you will be pretty fine near the base, then you should just manage your velocity so you arrive at Mach 1 about 8 km above the base. Approximately, use 20 km altitude, 150 km distance and Mach 3.5 as reference. I just use my stomach feeling for landings, when the target base gets too big too fast, I am in a bad situation and should drop the anchor.

 

[Gumdrop]

I suggest using gp's excellent Aerobrake MFD. This tool has improved invaluable for my atmospheric reentries. Combined with the attitude autopilots of the XR2, precision reentries are not hard to come by.

 

[orbekler]

I suggest using gp's excellent Aerobrake MFD. This tool has improved invaluable for my atmospheric reentries. Combined with the attitude autopilots of the XR2, precision reentries are not hard to come by.

Yep. Invaluable.
Also, no need of S-turns, (with XR-2, at least), just (sometimes) a small banking correction if you're a bit out of path.
But of course you should be already aligned with the base, and for that you can use BaseSync MFD.
Also, in Orbiter forum video section, you'll find several reentry clips.

 

[mode1bravo]

I don't really yet ballpark by velocity altitude or range... i just use the deceleration until I am about 150 km away from the base. if you go by 16 m/s² deceleration, you will be pretty fine near the base, then you should just manage your velocity so you arrive at Mach 1 about 8 km above the base. Approximately, use 20 km altitude, 150 km distance and Mach 3.5 as reference. I just use my stomach feeling for landings, when the target base gets too big too fast, I am in a bad situation and should drop the anchor.
07-02-11 09:13 AM

Urwumpe, thanks for the number references 20km alt 150km dist Mach 3.5 Mach 1 8k alt. That's what I was looking for. I will give it a try next time around.I noted my old profile versus your recommendation, turns out I was about x2 over it. Mach 7 and 12km higher at 150km distance. I'll fix this by removing or reducing the S turns and or letting the velocity bleed off a little more than 2.8kps at the same distance.

I suggest using gp's excellent Aerobrake MFD. This tool has improved invaluable for my atmospheric reentries. Combined with the attitude autopilots of the XR2, precision reentries are not hard to come by.

Gumdrop, I downloaded Aerobrake MFD. I guess being an LEO type never having went farther out than the moon it got overlooked. I assumed it was used for interplanetary entries in different atmos than earth or well "aerobraking" a la Leonov in 2010. My intent was to be able to do it manually first using only the attitude autopilot of the XR2 before turning it over to HAL most of the way in before taking over again for landing.

 

[Tommy]

There's no "correct" way to do it, but Urwumpe's way is fine.

I tend to come in a bit "hotter", especially if I'm coming in at a near right angle to the runway (often the case at KSC). In that case, I try to cross the runway line about 20k from the end of the runway. I'll keep the high AoA until I'm about 850 m/s velocity at about 20k altitude, hopefully about 25k short of the runway line. A second or two after I cross the runway line I'll turn AWAY from the runway, and make a HAC turn. Try to keep the G-force constant throughout the turn (between two or three G's), and as you lose velocity the turn will "tighten" and after turning about 270 degrees you will be fairly well lined up on the runway, about 14k altitude and with a good 15-20 degree glideslope to the runway.

An example of this can be found in the "Home Direct" tutorial (at Orbithanger)- which also demonstrates the inverted re-entry technique for direct re-entries from the Moon. NOTE: The latest XR vessels can hold AoA while inverted, so the manual adjusting of COG and trim is no longer needed.

 

[mode1bravo]

There's no "correct" way to do it, but Urwumpe's way is fine.

I tend to come in a bit "hotter", especially if I'm coming in at a near right angle to the runway (often the case at KSC). In that case, I try to cross the runway line about 20k from the end of the runway. I'll keep the high AoA until I'm about 850 m/s velocity at about 20k altitude, hopefully about 25k short of the runway line. A second or two after I cross the runway line I'll turn AWAY from the runway, and make a HAC turn. Try to keep the G-force constant throughout the turn (between two or three G's), and as you lose velocity the turn will "tighten" and after turning about 270 degrees you will be fairly well lined up on the runway, about 14k altitude and with a good 15-20 degree glideslope to the runway.

An example of this can be found in the "Home Direct" tutorial (at Orbithanger)- which also demonstrates the inverted re-entry technique for direct re-entries from the Moon. NOTE: The latest XR vessels can hold AoA while inverted, so the manual adjusting of COG and trim is no longer needed.

Tommy, I like your higher speed approach. You have to be
sharper to pull it off, less room for error. Something I'm trying to
work up to!

I guess I'll just follow up with the rest of the lower speed way
in from where I left off if anyone's interested. It works for me
now consistently getting me into KSC dead stick using only the XR2
attitude auto pilot, surface, map, and orbit MFD only.

Of course its an approximation since it always varies somewhat but
when Crossing Florida coast approx 2.4kps 38km alt just before
this I start a 60deg left bank till about mid way across the state
then reverse the bank 60 deg right. At 90 deg east heading
(approx) level out maintain your alt now 36km by slight pitch
input. Approx. when you get out over the water start the right turn
60deg using pitch. You will slightly lose speed constantly, the v
vector on the horizon.During the turn as speed drops you will
have to notch up the pitch trim to compensate.

This turn will take you out 180km or so overshoot of KSC, but no
worries as long as you don't get below 34km alt you speed wont drop
off too fast. Speed now 1.7kps 34km alt. Rolling out of the turn
on the runway heading 330 after a grand tour west and southwest
of Grand Bahama back up the Florida coast wings level now around
1.3kps 33km alt just enough pitch to keep you slowly losing alt till
your about (approx) parallel over the RWY just off the beach,
Let alt drop just below 30km alt dump remain RCS fuel get
off the XR2 attitude auto pilot speed now around 1.0kps.
when 80 km(approx)past the RWY initiate 180 deg left turn using only
.8 positive pitch trim for the turn on a 60 deg bank. Rolling out
of that sets me up real nice on energy to make the field at just
under 475TAS 24KM alt 70km dist.

Hope this helps some of the newer XR2 drivers. I had fun
figuring it out.

Thanks for everyone's input on this.