Tuesday, October 02, 2007

More Lunar Hopper

Here's a specific mission mass budget:

The goal on the lunar surface is to deploy three HDTV cameras with motorized zoom, pan, and tilt. The cameras shoot stills or video, record to flash, and then send their bits to the main transceiver over an 802.11b link. The radio links require line-of-sight and fairly close range, less than 1 km. The camera and radio are powered-down almost all the time, and the onboard battery has enough juice for perhaps five minutes of camera operation and maybe 20 minutes of radio time.

Each camera sits on a little post with three legs and an anchor that secure it to the lunar surface. The anchor is explosively shot a foot or so into the lunar dust, and then a spring-wound mechanism tensions the hold-down string. The hold-down string is to keep the rocket plume from blowing the post over when the lander jumps.

The mission is to land somewhere with a good view of the surrounding terrain, deploy one camera, look around a bit, upload pictures/video, and let mission control find somewhere interesting to hop, then jump there and deploy another camera. Then do that again. Then do a third jump, after which we just use the camera on the jumper. The idea is that the first and later second cameras can get video of the jumper taking off and landing, then send that video back to the jumper, which sends it to Earth.

The camera weight with zoom and pan/tilt sets the mission weight. I don't know anything about spaceflight-qualified hardware, but I've looked at the MSSS web site like many of you. A little Googling around makes it look like pan/tilt heads are pretty heavy, but these are designed for Earth weather and Earth gravity.

HD Video/still camera500 g4 watts
Zoom Lens650 g0.5 watts
pan/tilt head500 g0.5 watts
5 foot post and three legs400 g
explosive anchor and spring reel500 g
battery200 g
radio/computer250 g
total3000 g

Two of these, plus a pan/tilt on the lander are going to be about 8 kg. My guess is that the lander's radio link will be about 4 kg, and the dry mass of the vehicle necessary to land all this will be another 18 kg for a total of 30 kg.

Descent from lunar orbit, landing, and two more hops will take 2000 m/s delta-V. If we're using a N2O4/UDMH hypergolic motor with 2500 m/s exhaust velocity, then we'll need 37 kg of propellant when in lunar orbit.

I think you want to do the earth exit burn, lunar orbit injection burn, and descent and hopping all with the same motor. You do it with drop tanks, which probably get blown off after the first lunar deorbit burn. This gets the mass in low earth orbit to around 400 kg, which is well inside what a Falcon 1 can lift from Omelek.

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