Lunar Mission Sim

[Janus]

Originally Posted by CraigD

Wow!

Is the Strauss soundtrack a feature of Orbiter, or something you added, Janus. In either case, a nice touch.

I added the soundtrack and text overlays in "post production". I thought it was too dead with out some audio, and all the audio from the original recording had was background noise.

I didn’t notice any mid-course correction maneuver. Was this because there was none, or was it unnoticed due to the time compression? I recall from some of the Apollo data I’ve been using that, given the precision available to even modern spacecraft, a mid-course correction is a practical necessity.

Generally, most of the mid course correction is what is known as a "broken plane" maneuver. This correction aligns the inclination of the transfer orbit to that of the Moon. This is done by waiting till your trajectory crosses either the ascending or decending node of the Moon's orbit and then making a burn along the normal of the orbital plane. The rest of the correction is to make up for practical variations between the calculated and actual performance of the engines.

I eliminated the need for the broken plane maneuver at this point by starting from an LEO orbit with the same inclination as the moon, and since the sim is a theorectical model it doesn't suffer from the types of variations in engine performance a physical engine does. In the real world we would need to allow for such a mid-course correction.



So, to save me the labor (and test of my practical orbital mechanical skill ) of calculating them myself, can the Orbiter run produce a thrusts data (time, magnitude, and vector) in a simple text format. I’d like to plug it into XGRAVSIM4 and see how it works. And, of course, the data must be available in a form that can be used to actually program the control system of a spacecraft.

I can give you some of that info here. The engine thrust for the booster is 23206 Newtons, ISP 288 secs (These are based on a real world, off the shelf, solid rocket engine).
For this sim my intial fuel mass was 1324.7 Kg, of which, 5.2988 kg was used to make the attitude adjustment prior to main ignition, leaving a fuel mass of 13.4012kg. The empty mass of the booster was 147.4 kg and the payload (lander package) massed 500 kg. The booster ran till it exhausted its fuel which took 160.5 sec.
thrust vector was prograde to the orbit.

The separation of booster and lander package imparted a delta v of 1m/sec to the lander.(This is one of those time sensitive events, if the separtion doesn't happen within 1/2 sec of burn out, the package will miss the moon or will need a mid course correction later. )

Given that there are so many science and commercial satellites performing routine orbital maneuvers, there must be some standards for this sort of control data. Is anyone familiar with them?

[Janus]

Originally Posted by TheBigDog

In watching the video I could not tell how the sim was accounting for the transition from earth to lunar gravity. I was playing one of the games someone had posted a couple on months ago last night, the gravity pods game. I am hoping that the sim I built will eventually work something like that, only on a much grander scale. I will leave it to the experts to do the realistic sims, and give us an idea of the launch windows we should be looking at for optimum payload delivery.

I loved the Strauss touch too.

Bill

If you watch the display on the right after it switches to moon orbital reference you can see how the projected trajectory changes as the Earth to Moon trajectory progesses. Also, in the original right display is a function that will plot the trajectory taking the Moon's gravity into account.

[Janus]

As promised, here is the landing stage of the mission.

I picik the mission up at an altitude of 200 km and then procede with a gravity turn landing. I use a retrorocket package to kill most of the lander's velocity, which sparates away at about 8 km altitude, where the lander's egines take over. I did this because I needed a fairly powerfull engine to kill the velocity, but it was easier to land with smaller engines with finer control.

The little jump you see at separation is the veiwpoint shifting focus from the retro stage to the lander. I haven't quite figured out how to eliminate it.
The video also ends just a split second before actual touchdown. That's a post-production error that I missed.


Landing point is 2°E 1.25°N. On the Eastern edge of Sinus Medii (Central Bay), about 30 km East of Blagg crater. Just about smack dab in the middle of the nearside of the Moon.

From the point of ignition of the transfer booster to lunar touchdown the mission takes 4 days, 1hr, 7 sec. Date of launch chosen was Jan 30, 2008.

YouTube - X-prize lunar landing

[Janus]

Here's some screen shots from launch onward. The launch vehicle is based on the Eurocket. From top left clockwise: (1) launch (2) first stage separation (3) second stage separation (4) third stage and fairing separation.