Flight Question Looking for Mars landing advice

[EternalFrustration]

Hi everyone!
I'm trying to figure out how to land my DGIV at Olympus Base. What is a good
-initial altitude
-distance to base
-new periapsis
to get down in one piece?
All of the tutorials I've found seem to be out of date.
Thank you for any pointers,
-P

 

[worir1]

mars re entry is quite hard because of the low atmosepheric pressure so aerobrakig will be hard. i suggest you slow down as much as you can maby a PeA of - 600km so you fall strait down then use hover engines to slow before touch down

 

[PhantomCruiser]

If you are in a DG (or derivative) or anything with hovers, lean back and use those to decelerate. Once you are pretty slow, level back out and ride the hovers down as if you were on the moon.

LOLA had a demo of a DG landing at Olympus base IIRC. Watch it and mimic that behavior. Mars is tough because you've almost got the behavior of an airless body due to the thin atmo, with the problems that accompany an atmo (if that makes any sense). Basically you can't land it like a plane, gotta land like a cannonball.

 

[Ripley]

Take a look at the excellent blixel's tutorials on Youtube.

http://www.youtube.com/playlist?list=PL8A48A56E322B5F0D&feature=plcp

 

[blixel]

Take a look at the excellent blixel's tutorials on Youtube.

http://www.youtube.com/playlist?list=PL8A48A56E322B5F0D&feature=plcp

I appreciate the nod. I would also point to this recent video response I did which focuses just on the deorbit and landing portion.

I never call my videos "tutorials" really. They are just recordings of me playing with orbiter and explaining my thought process as I go.

 

[Ripley]

...I never call my videos "tutorials" really. They are just recordings of me playing with orbiter and explaining my thought process as I go.

That's why they are "excellent"!

 

[EternalFrustration]

Thanks everyone for your advice so far. I'm writing this from work where Youtube is blocked, so I can't be certain but I'll guess that I've missed those videos. I'll check them out.

FWIW, here's my sad story: I started from about 100 km altitude, at about a quarter of the way around Mars from Olympus Base. I burned retrograde until my orbit on the Map MFD hit the surface a little way past the base. I tipped back to 40 degrees AOA and prayed. By the time I got down to about 15 km altitude I had only gotten halfway there. So I used the autopilots to fly the remaining distance, dropping my speed and altitude in steps as I went. I overshot the base because I wasn't paying attention, then worked my way back. As I touched down on the pad, the screen tilted sideways - I had forgotten to put the landing gear down!

TLDR: Made it by the seat of my pants, only to fail at the last minute because of my own lack of attention to detail.

It's all worth it though, it's for my three and a half year old daughter who wanted to see Daddy fly his rocketship to Mars. A new little space nerd in the making!

Thanks again for all your help everyone, I'll let you know what happens next attempt.
-P

 

[statickid]

The way i do it is to manage a <35km reentry for a while, then fly any remaining distance maintaining a speed a little over mach 3-ish. when getting closer its safe to open retro doors because of the thin atmosphere. So I do a long retro burn until I lose aerodynamic lift while gradually replacing lift with hovers and eventually land like a lunar module. This takes alot of fuel sometimes, but I think it's ok for the DG. A more realistic approach would probably involve a chute or a strong last second hover blast so :shrug: I like the idea of high speed cruising on Mars and the DG has wings so might as well use 'em

 

[Urwumpe]

You should plan a much longer distance for slowing down, 90° is way too short, 150°-180° is better. Also, you need to put your impact point on Map MFD a fair bit in front of the base, you can glide a pretty long distance on Mars. Don't fly too long at 40° AOA, the low density of the Mars atmosphere permits a pretty good glide at low temperatures in about 10-15 km altitude.

 

[statickid]

yeah, when i say "fly the remaining distance" i'm talking about a long glide like Urwumpe is referring to, not a main thruster powered flight. Although if I'm falling short, I sometimes give it a blast or too to regain glide potential

 

[EternalFrustration]

Darn you and your excellent videos! You "made" me attempt aerobraking twice yesterday.
The first time, I don't know what I did wrong, but my PeA slipped up when I wasn't paying attention. I only got down to about 45 km, which was not nearly enough, and by the time I realized what had happened I was past periapsis and heading back out into deep space again. Reload...
The second time, I apparently came in too steep, the Hold AOA autopilot on my DGIV wouldn't engage and I plowed straight into the atmosphere and burned up.
Thank the Probe for quicksaves! I'll get it right eventually...

 

[Urwumpe]

Piloting...piloting...

"I was past periapsis and heading back out"... you are past periapsis everytime you are raising again...since you have lift, all you need to do is to bank until are flying level again.

 

[EternalFrustration]

Piloting...piloting...

"I was past periapsis and heading back out"... you are past periapsis everytime you are raising again...since you have lift, all you need to do is to bank until are flying level again.

Well, yes, I know that now... :facepalm:
I need some more practice and I'll get the hang of it. Meanwhile, lean back and have a good laugh at my foibles...

 

[Screamer7]

mars re entry is quite hard because of the low atmosepheric pressure so aerobrakig will be hard. i suggest you slow down as much as you can maby a PeA of - 600km so you fall strait down then use hover engines to slow before touch down

Which let me think: are the atmospheric parameters of Mars correct in Orbiter?
Curiosity was still at a high altitude when it performing the aerobraking maneuver.
And it decelerate at a high rate until the parachute open and decelerate it even more.
The same was valid for the MER's

 

[statickid]

it looks pretty good, i just did the following experiment.

Deorbit maneuver, with Pe of 11km. I kept AoA at about 50 degrees to avoid lift.

The xr-1 registered dynamic pressure at around 112km, according to curiosity decent profile, Mars atmosphere starts at 125km. I would imagine the VERY EDGE of the atmosphere to be quite thin. NASA describes the atmosphere as a thin gradient.

Dynamic pressure ramps up and xr-1 does most decelerating around 10-15km alt, Curiosity deploys the parachute at around 11km, still has ground speed of 400 m/s. In the XR-1, I managed my decent and can barely manage any lift <450 m/s ground speed, however, the drag doesn't slow me down much either, this also seems consistent.

It says that the heat shield separated at 8km, and the powered decent was released at an altitude of only 1.6km, still traveling 80m/s although i think at this point it was mostly vertical rather than ground speed.

From what I can tell the Orbiter model seems pretty realistic

 

[EternalFrustration]

Okay everyone, I'm having a hard time visualizing my problem to figure out how to fix it. My re-entry angle is too high, and the Hold AOA autopilot won't turn on. How do I lower my re-entry angle to under 2 degrees?

 

[statickid]

If you want a fail safe way, start with a low circular orbit of ... say... 120km. deorbit with a Pe of something low for Mars, something like 10km on the opposite side of the planet. Your reentry angle should be quite low

---------- Post added at 10:05 PM ---------- Previous post was at 10:00 PM ----------

or do it manually, or use an XR-1 which is basically a delta glider with XR control panel, or use an XR-2, because XR family has more options for atitude hold built in, or use atitude hold MFD. The DGIV reentry autopilot is quite picky and IMO seems optimized for Earth Reentry or at least places with thicker atmos

 

[Enjo]

I've made this some time ago:
[ame="http://www.orbithangar.com/searchid.php?ID=2434"]Mars atmospheric entry and landing playback[/ame]
It's a playback of the method described by statickid.

 

[EternalFrustration]

or do it manually, or use an XR-1 which is basically a delta glider with XR control panel, or use an XR-2, because XR family has more options for atitude hold built in, or use atitude hold MFD. The DGIV reentry autopilot is quite picky and IMO seems optimized for Earth Reentry or at least places with thicker atmos

Okay, now I'm learning the XR2. Takeoff from Earth is a whole lot more complicated, but very cool. We'll see what happens when I get to Mars.

 

[ADSWNJ]

Okay, now I'm learning the XR2. Takeoff from Earth is a whole lot more complicated, but very cool. We'll see what happens when I get to Mars.

It's a sweet ride once you get the hang of it. Get to 10km relatively quickly to get out of the heavy air, then smooth it out up to say 22-25km. Level out and get to Scram speed (3.5 Mach on the XR-2), then ride the edge of overheating the ship and getting the max thrust from the Scrams. Once they red-line at 7k temperature, shut the doors, throttle up the mains and get to orbit.