aerocapture at Mars using DG3?

[DL1DBY]

Hi,
has anybody succeeded in performing an aerocapture manouvre at Mars and survived (not too much G's or heat)? If so, I would like to know how to do it.

Thanks,
Dieter

[schumanna]

Hi Dieter,
            First of all welcome.  I'm no sure how many have tryed it.  It's very complicated.  best to check out Orbit
Hangar and download the right MFC for it and then read the docs.  Check out the manuale.

schumanna

[laserpithium]

I did it several times.
The main problem is to determine the value of your PeD near Mars. I don't know if tools to predict that exist, so I use
the test/error way.
I, for one, I choose, for a trip earth/mars a PeD of 19km. Use IMFD or Transx to do that.
When you are close from Mars (that is when your altitude reach 120 km), execute PRO104SPEC40 in the DGIII
computer (reentry programm).

If your PeA (altitude at your périapsis) is too low, you'll burn and crash. If it's too high, the brake won't be very
efficient. Just try 19km to start, it's usually good. If not, change this value of 1 or 2 km (no more !), and do it again !

If you succeed, do not forget to higher your PeA when you'll reach your ApD after the burn (else you will do a second
aero-brake... no good !)

Good luck !

Laserpithium

[DocHoliday]

I haven't tried aerobraking around Mars with DG3.. As far as I know it's not really.. possible. At least at survivable Gs.
I assume you are trying with the DG3, becuase most other craft don't care about Gs and heat (Shuttle A2 excluded).

I also assume you know how to do it. If not you can try the IMFD. There is a tutorial that sets you up for a
aerobraking pass with the stock DG. I am not sure if it's included with the IMFD zip or do you need to find extra
tutorials..

Anyway, the problem I see is, if you want to come from an inbound parabolic orbit into any kind of elliptical capture
orbit, you would have to brake quite a LOT becase you will pass surface below 20 km or so. Now the problem is, you
have to brake ENOUGH for the craft to come into an orbit that is at least Ecc <1 otherwise you miss the planet and
that's it.. This can all be calculated. I think SimonPro's excellent calc utility has provisions for this sort of passes.
Lemme see.. Here:
http://www.orbithangar.com/download.cfm?ID=587 (Lower right corner of the screen gives results that might come
handy for this sort of things) Not for G calc though..

Suppose you can reduce speed down to highly elliptical and not exceed 6 or 7G you should be able to get it to circular
in the next few orbits. If not, it can't be done You can also experiemnt with different entry attitudes once you get
close to periapsis. Since DG3 has wings they can be used to induce additional drag. Best effect is probably if you pitch
it up to 90 degrees and yaw it on its side (normal) to the orbital path. I don't know what happens if you turn it upside
down and pitch it up you might get funny results.. Either way, this will all increase G... Perhaps you might try
turning it retro and putting some engine thrust to work with that, but this won't be pure aerobraking then.. BUT, if
you engage engines above atmospheric level, no G will be registered as G in DG3 depends on atm. pressure, not
acceleration alone. At least I seem to recall so.

Good luck,

[Rocketeer]

Unless I am completely missing the issue, aerobraking and capture on Mars is fairly easy, and considerably easier
than on earth.

I find it pretty easy to atain an orbit around Mars using only aerobraking, even if you are coming in at 1,500 m/sec
above capture speed.  For earth, 1,000 m/sec is about the limit.   This is because of the unique (or at least different
from earth) atmosphere of Mars.  Although the atmospheric pressure at the surface of Mars is less than 1 percent of
that of earths, the Martian atmosphere extends almost as high as earths atmosphere (100km for Mars vs. ~140km
for Earth).  Hitting the atmosphere at capture velocity, you can get down to about 15 km on Mars vs only about 70 km
on earth before your toast! So you have more atmosphere to work with on Mars.  Also capture velocity is lower on
Mars than on earth, so you are going through the Martian atmosphere more slowly and have a longer time to
decelerate.

Of course, it all depends on your speed.  If you come in too fast to either you won't be sucessful.

laserpithium pretty much summed up the procedure.  Set your PeA to about 20 km, use P104s40. I've also found that
once you reach Periapsis, you can lower the nose below 0 degrees to help keep you in the atmosphere still longer.  It
is possible to attain a circular orbit below 100km in less than one orbit.

Hope this helps -

Love that DGIII - thank you, Dan and Martin.

Don

[DocHoliday]

Cool, so all my theoretical talk is not needed I'd have to try it. What kind of G do you get with your setup?

I thought if you go that low to the atmosphere you'd accumulate quite a lot of speed in any case. But in Orbiter Mars
atmosphere doesn't start at 100km but at something like 20km, so the braking will probably not start to happen
before that, unless you tinker with mars.cfg

Cheers,

[Shirson]

Scenario Aerobrake from pack IMFD.
Replaced DG to DGIII.
DG3Config Fuel Isp -> Realistic

1. Translation mode. Little acceleration for change reentry angle to 5.85 (2100 gramm from RCS fueltank)
2. Pro 104 Spec 0
3.  AOA 60, roll left to -90.
4. Cone temp 1200, roll zero, AOA 15

Airbrake done, DGIII on elliptical orbit around Mars.

5. Second pass. AOA 15
6. At ApD prograde for circular orbit.

ApD 5.163
PeD 5.150

MaxG 3.8
Max Temp 1800
Total fuel consumption: 257 kg.

[DocHoliday]

Wow!

I tried that a while ago, crashed and burned. 5.85. So that's the secret?

Way to go, thanks!

You should make a adventure scenario putting this into action Maybe time it so that one of the moons is on the
other side of Mars to be intercepted half an orbit after injection? Rescue a stranded bird.



Cheers,

[Shirson]

DocHoliday wrote:
Wow! I tried that a while ago, crashed and burned. 5.85. So that's the secret?

Intuition.

Way to go, thanks!
You should make a adventure scenario putting this into action Maybe time it so that one of the moons is on the
other side of Mars to be intercepted half an orbit after injection? Rescue a stranded bird.

Hm....
(starts think about)

[Rocketeer]

Doc, you can aerocapture as I described earlier with a max of 3 G's.  Again, it depends on your entry speed and
weight, but at 1,000 m/sec above capture velocity, it should be pretty easy.

[DocHoliday]

I'll try it. sometime I am immersed in another game right now, will have to wait, till I get fed up with it

[Simonpro]

I've tried it a couple of times, i usually fly in with the retros burning for a good minute or so, and then do a very low
pass (<500m) above mars. Get about 4g's and end up in a slightly elliptical orbit.
All good fun

[DL1DBY]

Hi everyone,
Thanks for all the advice how to perform an aerocapture manoevre at Mars. I just tried it this evening. I was coming in
with approx. 1.6 km/sec excess speed. I tried a PeA of 19 km, which resulted in an reentry angle (according to
Interplanetary MFD) of 5 degrees.  It went very well. Actually, it was a piece of cake. From 100 km above ground on I
was using autopilot reenty mode with 40 degrees AOA (PRO104SPEC40). The maximum G was 4.6 and the hull
temperature was well within limits. The Delta Glider achieved an orbit with an apoapsis of 5,500 km.

Amazing, isn't it?

Best regards,
Dieter