Flight Question Mars atmospheric re-entry

[thedopefishlives]

Hey all. I have more than a few Earth atmospheric re-entry trips under my belt, and I know that Earth's atmosphere is much thicker than Mars's and is thus able to slow me down from a much higher speed. My question is, is it possible using, say, the Delta-Glider to re-enter directly into Mars's atmosphere? Is it physically capable of slowing my ship down enough to land safely?

 

[Ark]

Sort of. The atmosphere can do most of the work, but you'll have to land vertically because it's too thin to support a regular runway landing.

 

[Cairan]

My question is, is it possible using, say, the Delta-Glider to re-enter directly into Mars's atmosphere?

Yes, but you have to go a lot closer to the surface to have an effect and successfully do a landing reentry. Ballpark figure for the DG is about 27 km altitude at periapsis. You also need to be very careful about your vertical velocity, you'll need to do very high bank S-turns, sometimes even inverted to a certain degree to have a lift vector keeping you within Mars' thin atmosphere or else you skip back out. Thermal management is critical.

Is it physically capable of slowing my ship down enough to land safely?

Yes, but as stated above, reentry and landing at Mars is VERY different. You'll never be able to glide down to the surface for an horizontal landing at a manageable horizontal velocity, you'll stall at supersonic speeds!

The best you can do is manage to be about 50 km from your target at Mach 2 and 5 km altitude, open up the retro doors and brake, while maintaining a low angle of attack. Once you've lost enough lift and you start to fall down to the surface, open the hover doors, and pitch up... The hover engines are a lot more powerful than the retro, but if you balance your pitch appropriately, the resulting vectors of thrust will null out your vertical acceleration while pitching up. Once your horizontal velocity is down to nothing, cut off the retros, and level off to the horizontal. You'll now land vertically using the hover engines.

That's about it... It's basically like landing on the moon except you can use the atmosphere for a substantial part of slowing down.

 

[Ark]

That's about it... It's basically like landing on the moon except you can use the atmosphere for a substantial part of slowing down.

This sums it up nicely. You don't have to do a full powered descent, but once you've bled off most speed and altitude the technique is the same.

IMO Mars is the hardest planet to land on, you can use LOLA or something for any of the airless bodies and Aerobrake/Basesync for Earth, but neither of them work all that well for Mars.

 

[sorindafabico]

On IMFD BaseSync, aim for ReA = 2.0 degrees, Ant = 10. degrees, Altitude = 8.0k.

Use AoA = 40 until vertical speed becomes > 0 (you're about 18k above ground). After that, change your AoA to control your vertical and horizontal speed at moment of landing - use AerobrakeMFD to control Hspeed at moment of landing and your landing point.

Of course, your speed will be too big for an horizontal landing. Open engine covers (check dynamic pressure first!), use retro engines to cancel your Hspeed and hover to control your descent rate. Wait the last moment to do that if you need/want to preserve fuel.

Recommended MFDs: IMFD (BaseSync to do MCCs to landing site), AerobrakeMFD, HoverMFD.

I landed the DGIV and the XR2 directly from earth using this procedure.

 

[Cras]

Just wondering, have any of you tried landing on Mars without using retros?

I have just killed the retros in my XR-2 config files, as I find them to be too much magic, and find the thrill of "getting it right" on moon landings quite exhilarating. But I was wondering just how hard it will be to try and land on Mars without them.

 

[sorindafabico]

Just wondering, have any of you tried landing on Mars without using retros?

I have just killed the retros in my XR-2 config files, as I find them to be too much magic, and find the thrill of "getting it right" on moon landings quite exhilarating. But I was wondering just how hard it will be to try and land on Mars without them.

Yes, once. I used the "Heli" mode of Hover MFD to assist me, but I spent more fuel (probably due to lack of practice).

 

[Cras]

I just started to incorporate Hover MFD into my XR-2 lunar landing procedure. That is a great MFD, and I find it so useful in just using it for the translational RCS capture stuff. I wonder how efficient you could get it using the "heli" mode, which does sound to do much of the same things you guys are trying, with the pitching and the use of hovers.

 

[sorindafabico]

To be VERY efficient, I think you must do some math, but HoverMFD does a good work when it says Hspeed is too high for linear thrusters.

 

[flytandem]

I've done hundreds of dead stick landings on Mars. Glide like on Earth. No retros. Then when you are as slow as possible and the nose is pitching up and you are nearing the limit of being able to keep it off the ground, turn on the RCS and you get an increase in pitch response allowing to be able to be more precise and also to get the nose higher. All the while floating just a few meters above the surface. If you don't have much fuel, you should be able to touch down with groundspeed of well under 300 m/s.
I use reentry mfd and shoot for a required decel of 1.2 m/s/s while doing the most of the glide in the atmosphere but as I get down to the last 3 to 5 minutes of gliding I let it start rising by having actual decel of 1 m/s/s or less wheels retracted and air brake in if necessary. The trick is to both keep it off the ground (barely) and watch the required decel. As the required decel gets above 2 m/s/s and on its way to 3 m/s/s, then let the ship gently touch down but remember to have wheels down . The wheels have bout 1.8 m/s decel wen rolling. So just lightly touch the brakes when required decel climbs to 4 or 5 m/s/s to bring it back to 3. Soon the base will be appearing and you should be able to roll conveniently onto a pad. YMMV.

 

[Rtyh-12]

Yes, in Orbiter that works, but in real life you couldn't simply roll on rocks and dirt at 300 m/s, or even fly 'just a few meters above the surface'. Is that right, or am I missing something?

 

[dgatsoulis]

In real life you'd also not be flying an XR2 to Mars, so... it depends on the level of realism you want.
Flytandem's technic is very useful, if for example you have a reasonable sized runway near your Martian base. you can stop the spacecraft in less than 2 km after touchdown.
Lining up with the runway is, ofcourse a completely different matter that takes a lot of skill. Just my :2cents: