Flight Question Technical question on a flight plan.

[PaulG]

Here is what I want to do:

Eject from Earth, go to Venus in the DGIV, orbit a bit, and then go back to Earth. Assuming I have enough oxygen for 2 years, I want the most fuel efficient path possible (NOT doing a Hohman transfer though, too long)

Here is my idea, can you please offer any technical or procedural advice on whether the logic is right in this flight plan?

When in orbit around earth, fire prograde to bring the ApA as far as possible, meaning, increase Ecc until 0.8 or so (obviously not => 1). Then, perform an ejection using a slingshot (around Earth) which is most favored for dV.

This idea seems to work pretty well, it saves me a bit of dV.

Then, is it possible to use the venutian atmosphere to help slow me down (without burning up) so that the Ecc will be less than 1 or am I stuck doing an orbit insert?

Thanks for the advice,
Paul

 

[Tommy]

It can save you some fuel. I wouldn't call it a slingshot since you aren't gaining any velocity from the earth's gravity, or changing your vector. It saves some fuel by allowing you to concentrate the burns closer to your Pe, where the higher velocity helps. It will work even better if you "pump" up the Ap over the course of several orbits, a bit at a time. You'll have to plan carefully so that your Pe is at the ejection point, and you reach Pe at very close to the optimal ejection time. If you need to make a plane change before ejection you may save a bunch of fuel if one of the nodes is at, or near, the elevated AP.

As for the aerobrake, it depends on what you're flying, and how you fly it. A DG style craft can be flown inverted to stay in the atmosphere longer and shed more V. Even if you can't get the Ecc below 1, it will save fuel in the insert burn.

 

[PaulG]

Thanks. If I fly inverted won't the temperature get too high?

As for the node change, I'm aiming for an equatorial inclination. I don't know any where else to change it except close to the node right near venus. Any ideas?

Thanks!

 

[Tommy]

Flying inverted doesn't really change the heating compared to upright, but if you use the low AoA you won't slow down very fast so keep your vertical speed close to zero. A descent rate of more than 10 - 20 m/s can get you in trouble pretty quick. Also, a low AoA tends to heat the top hull more than a high AoA, and it does have less shielding so keep a close eye on that.

As for the plane change, if you're using IMFD for this, after you set up the Course Plan and pick your ejection date, you can use Surface Launch mode to enter the right plane for ejection. IIRC IMFD and transX will both show plane change info while in the parking orbit. A lot depends on which transfer method (source plane, target plane. two plane, etc) you are using. Use whichever one needs the least DV.

 

[Scarecrow]

Thanks. If I fly inverted won't the temperature get too high?

Not if you do it right. The trick is to put your periapsis at a good altitude (determined through trial and error) when you're approaching the planet. Fly in an attitude with the nose pointed towards the ground, and the bottom forward, probably at an angle of attack of 40degrees. When you're about to enter the atmosphere, open up the Surface MFD. You should see your Vertical acceleration positive, since you're approaching your periapsis. Use the lift from your wings to cancel this out and keep it 0, and hold your favorite altitude. If you want to accelerate down, pitch down (lower AoA) so you get more lift, and bite into the atmosphere harder. Pitching up gives you less lift, and so your orbit will carry you up. It should be relatively straightforward from there. Just flip over and get some positive lift when you want to get out of the atmosphere again, or when the other end of your orbit gets into the atmosphere.