Flight Question Reentry at 40 Mach

[Gerdih]

Okay guys, been 3 hours trying this:

Coming from Mars ready for reentry Earth's atmosphere with an XR2. Reentry initial velocity is 40-43 Mach. I have been unable to land at the cape, I explode at 38 Mach / 60 km or I bounce on the atmosphere.

I have been trying reentry angles from 6 to 0 and I dont wanna use any motors to help. I have even desperately tried inverted reentry ( with heat shield facing space) to avoid bouncing but I am unable to land.

Any ideas? Do you think our poor XR2 is unable to do this on every imagined way?

 

[Cairan]

Do you think our poor XR2 is unable to do this on every imagined way?

Spot on. No possible way, you are going to breach the heatshield no matter what you do... Don't forget that your kinetic energy at mach 40 is going to be 4 times what is is at mach 20... and you have to dissipate it half as much time, so yeah... No way.

 

[statickid]

What about an incremental approach? Is it impossible to just slow down enough to get captured and then re-enter a week later when you come back around?

 

[MaverickSawyer]

What about an incremental approach? Is it impossible to just slow down enough to get captured and then re-enter a week later when you come back around?

Yeah. It's called a propulsive capture burn.

That said... If you were to light the mains about 20 minutes or so before entry, and burn through about 80% of the remaining dV, you MIGHT survive the entry.

 

[jedidia]

or I bounce on the atmosphere.

You could try bouncing it in a way that you'll hit it again when you come around next time... though at Mach 40 that won't be easy to do either.

 

[Urwumpe]

Okay guys, been 3 hours trying this:

Coming from Mars ready for reentry Earth's atmosphere with an XR2. Reentry initial velocity is 40-43 Mach. I have been unable to land at the cape, I explode at 38 Mach / 60 km or I bounce on the atmosphere.

I have been trying reentry angles from 6 to 0 and I dont wanna use any motors to help. I have even desperately tried inverted reentry ( with heat shield facing space) to avoid bouncing but I am unable to land.

Any ideas? Do you think our poor XR2 is unable to do this on every imagined way?

What about using the following techniques:

First of all: shallow re-entry angle. Try to stay above 85 km

Next, skip re-entry: Just slow down at high altitude long enough that you are just captured in a Earth orbit. Leave atmosphere again at a shallow angle (since the angle at which you leave Earth is also the angle at which you reenter Earths atmosphere again)

I don't know if it works at Mach 40 - the critical question is how much can you slow down from hyperbolic orbit to elliptic orbit before having to skip out, you only need to get rid of about 1,500 m/s from Mach 40 (11.500 m/s) to a stable highly elliptic orbit (10,000 m/s at low perigee). The XR2 should be able to bank fast enough for a controlled skip re-entry, but I don't know if you can slow down by 15 m/s² for 100 seconds without overheating or control the spacecraft altitude at lower decelerations.

 

[C3PO]

I don't know if it works at Mach 40 - the critical question is how much can you slow down from hyperbolic orbit to elliptic orbit before having to skip out, you only need to get rid of about 1,500 m/s from Mach 40 (11.500 m/s) to a stable highly elliptic orbit (10,000 m/s at low perigee). The XR2 should be able to bank fast enough for a controlled skip re-entry, but I don't know if you can slow down by 15 m/s² for 100 seconds without overheating or control the spacecraft altitude at lower decelerations.

IIRC the XR2's behavior changes quite a bit depending on the vehicle mass. You could try dumping most of the fuel/cargo to see what the upper limits of reentry are.

 

[Gerdih]

IIRC the XR2's behavior changes quite a bit depending on the vehicle mass. You could try dumping most of the fuel/cargo to see what the upper limits of reentry are.

I thought about that, after an efficient travel I still got 48% +- (3%) main fuel depending on the final approach maneuver.

On the other hand I think the best I could do is a burn for an elliptical orbit and try to land at the Cape after that. I guess the period should be 24 hours and I would have to do another maneuver to change Inclination.

Is it right? Does anyone who tried this before could give me some advice?
I always use IMFD by the way

 

[boogabooga]

This is useful for determining periapsis altitude:

http://www.orbiter-forum.com/showthread.php?t=34197

 

[MaverickSawyer]

I thought about that, after an efficient travel I still got 48% +- (3%) main fuel depending on the final approach maneuver.

On the other hand I think the best I could do is a burn for an elliptical orbit and try to land at the Cape after that. I guess the period should be 24 hours and I would have to do another maneuver to change Inclination.

Is it right? Does anyone who tried this before could give me some advice?
I always use IMFD by the way

Okay, yeah. With that much fuel, don't hesitate to burn some of that off to slow you down. I'd use about half of it to get you to a more reasonable speed before atmospheric interface.

 

[Cairan]

Just for the records, I was stating that at Mach 40 a survivable reentry and/or aerocapture is just bluntly not possible in the XR2, IIRC... However, the procedure described by Urwumpe is the one I use when I come back from Saturn... and to be closer to 12 km/s than over 14... First, as much as possible, do a Hohmman transfer with a minimum arrival delta-v... even if it requires more overall delta-v, and more delta-v at Mars ejection...

Then when you get to Earth, fire almost everything you've got left in the tanks to reduce your periapsis velocity... If you can slow down from 13.6 km/s to even 12 km/s, that's going to reduce your peak heat load by almost 30%... then you can scratch another km/s to get captured in a highly elliptical orbit... Be careful not to have an orbit that takes forever to get back to another pass in the atmosphere...

As others have observed, inverted, shallow and high is the way to get aerocaptured... when you are in orbit, go deeper and steeper...

 

[Gerdih]

Finally done a burn to an elliptical orbit with a period of 24 hours, tried a reenter but it was too quickly, survived it reaching max. temp. at nose about 2800 Cº.

Maneuvered to try again on the next pass.

Max nose temp have been 2100 Cº, 7 minutes of nice plasma show and about 12 minutes of atmospheric flight. The autopilot turned a little bit crazy and I got 85% damage on an elevon and had to fire engines for the lasts 2 minutes to mantain a velocity of 190 m/s.

Landed at Cape Canaveral when Engineers where waking up at their homes!

P.D.: any way to fix the elevon while playing?

 

[Buck Rogers]

Some time at the end of last year someone else posted a similar question which reminded me how cool inverted direct reentry is, actually IMO it's one of the coolest things one can do in Orbiter! So I did a quick trip to the Moon and came back with an Orbital V. at Pe: 13k+, PeA: 75k, ReA: ~1°, Ant.: ~90°, atmospheric contact with Mach 46+! The trick is very fine AOA corrections, and glow to the limit!
Here's a playback of the XR2 inverted direct reentry, night landing at the Cape, final approach could have been better! Reviewing the playback it looks like there's room to go in even harder, I challenge anybody to try!

P.S. I don't know about in game, but you can exit and change the damage section of the scn. file and reload...

 

[statickid]

Yeah. It's called a propulsive capture burn.

That said... If you were to light the mains about 20 minutes or so before entry, and burn through about 80% of the remaining dV, you MIGHT survive the entry.

I was talking about something like Urwumpe is describing a few posts down, skipping reentry on the first go and trimming off velocity in the upper atmosphere in order to get into a manageable elliptical orbit.

 

[tommo965]

Here's a playback of the XR2 inverted direct reentry, night landing at the Cape

Just watched your playback, nice one mate. Probably beyond my current skills I'd think but hey, only one way to find out! Cheers.

Sent from my GT-N8000 using Tapatalk

 

[Buck Rogers]

Just watched your playback, nice one mate. Probably beyond my current skills I'd think but hey, only one way to find out!

Thanks, like the attitude, practice makes perfect, and hey, in RL you'd only get one chance, in Orbiter you can do it again and again and again, just for laughs!
I think there's nothing more satisfying than pushing the limits of the theoretically feasible riding the knifes edge between the fires of hell and the oblivion of space, plasma a few centimeters below your arse and the blue sky of home sweet home above, knowing that every tiny mistake could mean instant death!
I remember my first simple reentry attempts were daunting, have you given it a go already?

@GERDIH: Did this answer your question/ help you further?

P.S. I'm not advocating that this is the most sensible method, catching orbit first would be much safer! But its nice to know one can if one's mad enough/ or have no other choice.

Saddle up and ride like there's no tomorrow! BR

 

[Gerdih]

Have been some months without playing and I am relearning. Maybe this method would be dangerous to use right now for me. I will try it in some weeks though, I am doing reentries and atmospheric flights recently.

P.S. Awesome playback!

 

[Buck Rogers]

Yeah I know that relearning feeling, always get a bit of a shock coming back to Orbiter!
Have fun riding the waves of fire...

 

[Cras]

Inverted re-entry is not that hard anymore. It used to be very hard since the attitude autopilot didnt work for inverted bank angles so you had to mess with the CoG on your own to keep it stable, and also finding where to hit the atmosphere using IMFD so you are on the right path towards your target runway.

But with LTMFD, planning that is quite simple (if you are coming from the moon anyway), and inverted attitude hold is much easier to do now you can set the bank to 180 degrees in the XR2 autopilot. I do them quite often and they are pretty much just as simple as a normal re-entry. A little harder I suppose since you gotta stay on top of your vertical speed a bit more but really, practice makes perfect. Just try it out and soon you will be able to do them in your sleep, trust me.

 

[dman]

What about "Skip Rentry" - similar to that used by the 1960's Zond probes in
returning from the moon

While Zond probe were unmanned the later ones practiced skip reentry,
supposedly for a manned mission from the moon

The Zond were first hit the atmosphere over the south pole, bounce back into
space to altitude of about 400 km then do second reentry for a landing