Flight Question inverted re-entry?

[Salun]

Heres a challenge. Trying doing it in Venus's atmosphere. Its nuts O.O

 

[Tommy]

I found that 63 to 65 K is the optimal PeA to aim for when heading in.

At what velocity? If you are returning from the Moon you;ll have a velocity of about 10.3 km/s. At that velocity an XR will burn up before you get down to 65k - a PeA of around 72k is survivable. Coming in from Mars, you'll want a bit more altitude - around 75k - 76k.

 

[Salun]

In my experience at 75 K you only get an aerobrake and bounce out of the air. 65 to 63 seems to work for me. Whats your intail AOA when you enter EI?

 

[Urwumpe]

In my experience at 75 K you only get an aerobrake and bounce out of the air. 65 to 63 seems to work for me. Whats your intail AOA when you enter EI?

Which is why we are talking here about inverted (= with negative lift) reentry.

 

[Wishbone]

Methinks this is one of the reasons I should write a calculator of AoA and bank angle that give maximum drag for a constant (at first, zero) vertical acceleration.

 

[n72.75]

As long as you have consumables to last you a while, all you have to do on your hyperbolic Pe., is make your orbit elliptic. On successive passes you can circularize your orbit bu dragging through the atmosphere.

On a hyperbolic return from the moon I did recently this was my aerobreaking plan. This was with a DG-IV

(65k) hyperbolic orbit ---> aerocapture 60° pitch
(60k)x(65M) elliptic orbit ---> aerobrake 60° pitch
(60k)x(25M) elliptic orbit ---> aerobrake 60° pitch
(55k)x(10M) elliptic orbit ---> aerobrake 60° pitch while banking from -90° to +90°
(55k)x(1.2M) elliptic orbit ---> aerobrake 50° pitch while banking from -90° to +90°

Several burns to align orbit plane for landing, and to get a PeA of 20k with a reentry slope of 1.1°.

I was used a deltatug to get to the moon and realistic fuel settings as well as mark I engines. I still had to drop about 3000kg of fuel before landing.

 

[Urwumpe]

Methinks this is one of the reasons I should write a calculator of AoA and bank angle that give maximum drag for a constant (at first, zero) vertical acceleration.

Actually, you usually optimize AOA for maximum L/D, unless you have thermal constraints. You can NEVER have too much hypersonic L/D. Never. The longer you can glide, the more control you have over your reentry and the safer it is.

EDIT: From following the thread...what about founding a "sort-of-a-VSA", the "Orbiter-Forum Flight Test Services". Just some sort of semi-professional test pilots for add-ons and stock vessels. Nothing too extravagant, just some loose group of people working together under common testing and documentation standards.

 

[Wishbone]

Gliding AoA calculation at zero bank is too easy (while the non-zero bank case is computationally equivalent to the inverted reentry scenario). It is indeed thermal regime I'm worried about - given the narrow reentry corridor (from max allowed heat flux and g constraints), the calculator should output (and ideally AP should hold) the requisite angles.

EDIT: Re - Test Services. A neat idea, but I'd like to automate testing as much as possible (the code already finds out which vessels don't have airfoils defined).

 

[Tommy]

Whats your intail AOA when you enter EI?

Initial AoA of about 40 degrees, inverted. When VS gets up to zero, adjust AoA to maintain zero VS (often means lowering the AoA a bit. Another method is to use an intitial AoA of 30 degrees, and a 90 degree bank angle - use roll adjustments to maintain VS - useful when you have some crossrange to target - or are uncertain of the altitude you need since you can roll to less than 90 degrees and get some upward lift if you are coming in to low.

An example of the first method can be found here:
[ame="http://www.orbithangar.com/searchid.php?ID=3660"]Home Direct[/ame]