Flight Question Reentry and landing with XR2 and other spaceplanes - is there a secret to doing it?

[Wishbone]

Just you wait until Dr."M" has implemented landing in a rain squall...

 

[Pipcard]

I only bank just to get my ground track over the base. I change the AOA to control descent. Is that okay?

 

[Turbo]

I dont use any of those MFDs for reentry. Im old school I guess, just using Map MFD and Surface MFD after my Deorbit burn. I find in the XR2 to do my burn at 18.3M from the base I intend to land at (Earth at around 400km, burn to 55km). Keeping a constant decent rate of 95 - 100 m/s, adjusting AOA and banking as needed, I end up where I want to land everytime, and have never burned up (so far). It took some practice to get down, but now I can land where I want 99% of the time, with an occasional 50km miss

 

[Spacethingy]

Woohoo! Just followed Jarvita's advice! It works awesome! :woohoo:

Here's my guide to what to do (well, it worked once anyway... :shifty:

1) When in an orbit of 300-400 km, get in the same plane as your base. BaseSync MFD (right at the bottom) is perfect for this, showing you how close your orbit comes to the base. You need to follow the instructions really. If you're not bothered about fuel/numbers, just do it by eye using MapMFD zoomed in as much as possible.

2) On the orbit that goes over the base, make your reentry burn when you are exactly(ish) on the opposite side of the planet to the base. Sounds naff, but works for spaceplanes well. You can tell this using BaseSync MFD or MapMFD. Use OrbitMFD, and stop burning when your... errr... lowest bit of your orbit is about 40km up. (I can never remember the names...)

3) You're now coming in. Don't use MapMFD to judge where you're going to land! It ignores the atmosphere and so gives wildly wrong readings for the land site (small square at the end of the orbit lines). Use the marvellous [ame="http://www.orbithangar.com/searchid.php?ID=2139"]AerobrakeMFD[/ame]. It does loads of complicated reentry stuff, we just want the map bit. By pushing various combos of the MOD and PG buttons, find something that looks like MapMFD with a little map inset. This is it! It shows your glideslope, taking into account the atmosphere.

4) Point your ship forward. Use whatever Attitude autopilot you have and point your ship with a AOA of about 45 degrees. Make sure things like nosecones are shut... :lol: By about 100 km up, put yourself in "reentry" thinking mode. We're going in.

5) As you reenter, keep an eye on AerobrakeMFD. Watch how your orbit land site suddenly shoots shorter and shorter. The inset map shows a zoomed in view of the base; use it to keep the end of the orbit/glideslope on the base. Each square is about 100 km across. Pitch up and down/ left and right to fine tune your glideslope in.

As a rule of thumb, a vertical speed of above 100m/s in dangerous - you'll heat up too quick to recover and.. well... let's say your base will have a nice impromptu shooting star display...

6) By 20 km up, you should be close enough and slow enough to switch to aeroplane mode, exit your autopilots and land your ship.

Phew.

 

[Tommy]

Also, most rentry tutorials are for the DGIV/DGIII for some reason. I want one for the XR2.

The only real difference is in the operation of the auto-pilot. The methods are exactly the same. The XR's auto-pilot is quite straightforward to use, and the XR series manual documents it's operation quite well.

I only bank just to get my ground track over the base. I change the AOA to control descent. Is that okay?

Where do you get your "heading alignment cylinder" from?

Using AoA alone to adjust the descent is fine - I do it myself. IRL there are two reasons the Shuttle uses a fixed AoA and uses bank to control the descent.

One is that the wings and tailfin act like the feathers on an arrow. They try to force the Shuttle into a low AoA nose-first attitude. This effect is most pronounced at about 25 to 30 degrees AoA - at higher AoA's it's less. This means it's far easier, safer, and efficient to maintain the 40 degree AoA and adjust the bank.

The second is that the Shuttle deliberately maintains a bit more energy than it needs - as a safety margin. After all, at high altitudes winds can exceed 300 kph - which could result in the shuttle coming up "short" if it's a head-wind. Add in variances in pressure, etc. The S-turns allow a way to bleed off energy when needed - or maintain it if needed.

The HAC is used for two reasons (IRL). One is that the Shuttle often comes in on a heading with a rather steep angle to the runway, which means you would need to turn on to the runway heading well before you are in visual or instrument (HSI/VSI) range. The second - even more important reason - is that it is used to bleed off the "safety margin" of excess energy. The HAC can be "loosened" or "tightened" depending on the amount of energy that needs to be shed.

There is an example of a "seat of pants" HAC in the Home Direct tutorial:

[ame="http://www.orbithangar.com/searchid.php?ID=3660"]Home Direct[/ame]

If you have IMFD Full Manual, that same flight recording is in there as the Moon-Earth Direct Return tutorial. It's a bit dated - LTMFD provides a better way to time the TEI, and the XR's autopilot now supports inverted flight so you don't need to manually adjust the COG and trim.

After the inverted portion of the entry, the methods used are exactly the same as a "normal" re-entry.

 

[Pipcard]

Finally, I did it!

I started at 200 km alt, did a retro burn (half an orbit to my landing site) and fine-tuned it so that it would pass near my target base, in this case, Cape Canaveral. (used AerobrakeMFD's Path (self) function)

I set the XR2's attitude autopilot to about 40 degrees AOA. The hull temps never got too hot. I used AerobrakeMFD's map function so that I can fine-tune the AOA. I also changed my AOA during the descent so that the vertical speed wasn't below -100m/s.

At about 30-20 km alt, I disabled the attitude autopilot, turned on AF control, and turned off the RCS.

I manually flew to the runway. At about 15 km alt, I deployed the aerobrake. When I got slow enough, at an airspeed of 200 m/s, I closed the aerobrake and deployed the gears. I used the VASI lights near the runway to help me land. When I was very close (less than 100 m alt) from the runway, I pitched up, and made a touchdown without breaking the landing gear.

The only MFDs I needed for the actual re-entry and landing were the Aerobrake and Surface MFD. BaseSync to help me see the closest approach.

Now I can get rid of the part of my signature that says, "I'm terrible at re-entry and landing." I may need more practice (I made quicksaves), and I haven't successfully landed on the Moon, yet, but now I successfully deorbited, re-entered, and landed on a runway.

Thanks, all of you, especially Spacethingy!

 

[Jarvitä]

and I haven't successfully landed on the Moon

Interesting, that's usually considered easier than an atmospheric landing, since you don't have to worry about AoA, skipping off, burning up, etc.

 

[Pipcard]

Interesting, that's usually considered easier than an atmospheric landing, since you don't have to worry about AoA, skipping off, burning up, etc.

The problem is slowing down at the right time.

 

[jangofett287]

yea, but theres no atmosphere, so where mapMFD/Basesync/whatev. says your going to touch down, that is where you will touch down. just open the hover doors to stop yourself smashing into the pad, and retro to avoid overshooting it when you fire the hovers (screw retro thrusters, no atmo so just point the ship!)

 

[orbekler]

With XR vessels it's quite easy to moon land, cause you got the Autoland feature, you'll never crash with that.
It's a pure ballistic fall, so Map MFD groundtracks will tell you exactly where you're going to touchdown.

This is one of my earlier moon landings:
[ame="http://vimeo.com/19595735"]http://vimeo.com/19595735[/ame]

 

[Tommy]

BurntimeCalcMFD (think that's the name - not at home) will calculate the distance you will travel during the breaking burn. You select the engine (main, retro, hover, etc) and input the delta -V (which will be your current velocity), and it will tell you how far you will travel before you stop. Makes timing the burn easy.

 

[Pipcard]

Now, I did a 4-day mission in the XR2:

From Wideawake to ISS to Wideawake. I landed in the middle of the night, by the way.

 

[Ripley]

I just started looking around at ships "other" than the usual DGIV-2 (time and RL®), and following your info on this post I finally managed yesterday to do a quick eyeballed Ravenstar reentry for the first time, starting from the scenario "XR-2 docked to ISS"!!

I did some DGIV-2 reentries before, so I know the procedure.
Me and my crew died from hypoxia, but this is due to the fact that I was a bit too short, I had to fly a long way to the base, and mainly that...I don't know the XR-2! I had to find out where the autopilots and the temperature display were, and so on...coolant temperature triggered a warning too at some point...

Anyway I survived the atmospheric reentry, the high temperatures, and I was in normal atmospheric flight when I died, so from my noobish point of view, it was a success!

So I must confirm that XR-2 IS forgiving!

:hail:

...I couldn't find any good reentry tutorials.

This thread could be the start of it.

 

[Cras]

My method has been using Aerobrake and Basesync for most spacecraft, the Antares Caspule, XR-2, DGIV, but for Shuttle Fleet I use Glideslope. Haven't tried Glideslope with anything else yet, but plan on trying it with the XR-2.

I am very interested however in trying IMFD for the deorbit, since it is such a powerful tool. I find Basesync and Aerobrake do not agree and have to sort of use a mean of both to get close to the base. I tried to set up IMFD but got nothing useful out of it in terms of when to burn and the attitude of the burn. This was using the base approach mode set to re-entry from a 220-220 km LEO. Can someone walk me through how to get a good solution with IMFD for deorbit?

 

[orbekler]

My method has been using Aerobrake and Basesync for most spacecraft, the Antares Caspule, XR-2, DGIV, but for Shuttle Fleet I use Glideslope. Haven't tried Glideslope with anything else yet, but plan on trying it with the XR-2.

I am very interested however in trying IMFD for the deorbit, since it is such a powerful tool. I find Basesync and Aerobrake do not agree and have to sort of use a mean of both to get close to the base. I tried to set up IMFD but got nothing useful out of it in terms of when to burn and the attitude of the burn. This was using the base approach mode set to re-entry from a 220-220 km LEO. Can someone walk me through how to get a good solution with IMFD for deorbit?

I may be wrong, but IMFD to me is not the proper tool to deorbit. You could try the Delta Velocity, but nothing will help you in taking into account dense atmospheres drag, nor the precise point of landing.

BaseSync will roughly get you in the proper path, then Aerobrake will fine tune. It's a solid and safe method.

 

[Cras]

I agree that BaseSync and Aerobrake is a solid way of doing things, especially when I used it for the Xr2 and the DGIV. It starts getting a bit more fuzzy when using it with capsules, (with Antares I aim to land at Edwards AFB, and find it to be one of the most difficult re-entry jobs I have attempted),

however Urwumpe has suggested on several occasions that IMFD can be used as a solid tool for the de orbit ops, and so I figured I would do diligence and give it a look, but I am stumped.

Upon Wishbone's suggestion in another post, I tried IMFD for ISS rendezvous (normally I use Rendezvous MFD), and did so with great results, so I am sort of in the mood for using IMFD for things other than getting me from Earth to another planet.

 

[Urwumpe]

Stumped? It is just telling IMFD where your entry interface is relative to the base... IMFD has many options, but most of them are not interesting for reentry anyway and better left untouched.

 

[Cras]

Stumped? It is just telling IMFD where your entry interface is relative to the base... IMFD has many options, but most of them are not interesting for reentry anyway and better left untouched.

I get stumped because it doesnt seem to be telling me a solution.

In the base approach screen, I target the base, set how I want to re-enter, and then it just says, burn now for 60 seconds. The burn time seems independent on my position over the Earth nor the time till I pass the base so I concluded that I am doing it wrong.

 

[Tommy]

IMFD won't help you to PLAN the re-entry, but it can help execute it. IMFD's Map can be handy - if you set a landing target on the main config page. Then, in Map, you can change the mode to display values that come in handy. "Ang" will tell you how precisely your current trajectory is to the target - but doesn't account for atmospheric effects and braking. It can also show you where your Entry Interface is, so can be a bit helpful on tuning the de-orbit burn.

That said, IMFD still isn't that useful for atmospheric re-entries. It will NOT make the de-orbit burn for you (at least not with any good efficiency).

You will get better results from BaseSync if you use it properly. The final alignment burn should be made AFTER you de-orbit (you should still be around 150k when you get to the last quarter orbit). When you de-orbit, it changes your velocity and period, so the "old" prediction is no longer correct.

 

[Urwumpe]

BaseSync is the completely wrong program there, you have the right mode among the "Course" menu, but I am currently not sure how it was properly called...need to start Orbiter.