Another one emerging from the vast Planetary Radio archives. Emily in her inpersonation of Sandy Moondust sitting on MER-B before launch (check the Astrobots project if unfamiliar with that ) said that it was to be launched on a heavier vehicle than MER-A, namely Delta 2 heavy with strap-ons 6" thicker than a regular Delta 2. Why is that so? Why launch two identical rovers on two different rockets? And - was it also the case with the Viking and Voyager pairs?

Because the launch windows were non-overlapping (mostly because of workload on the spacecraft and Delta teams) and for the 2003 geometry the C3 (a measure of injection energy needed to get to Mars) was rising rapidly at the end of the window (see
http://trs-new.jpl.nasa.gov/dspace/bitstre...5/1/02-1854.pdf ) MER-B needed a larger rocket.

The Vikings were launched on identical Titan-IIIE/Centaurs as far as I know. I suspect the Titan had enough excess capability to make up for any C3 differences across the window. It might be that in the days of routine dual spacecraft missions they had larger launch teams, also.

IIRC, they had to launch the Deltas from the same pad, so there had to be a separation of several weeks between the launches. At the beginning of the launch window to reach Mars in 2003, the amount of energy required to get a MER to Mars was within the capabilities of the more basic Delta II configuration. But by the end of the launch window, the energy requirement was enough greater that the Heavy configuration was required.

The problem, I believe, was more that the MERs stretched the ability of the Delta II right up to its limits. You oculdn't send anything much heavier than the MER package to Mars on a Delta II in any configuration. They nearly maxed out the launch and EDL systems with the MERs.

-the other Doug

No. There are two pads at Complex 17. MER-A went from one and MER-B from the other. The end of MER-A's launch window and the start of MER-B's were only about a week apart.

OK, kewl. I know that Oppy got off literally at the very end of her launch window, as well, due to issues with (among other things) debonding of cork insulation around the booster. IIRC, Squyres made the comment at one point that no one ever proved that the cork actually stayed bonded to the vehicle during flight, and that they might have left a trail of cork pieces all along the Atlantic Missile Range...

-the other Doug

Not really the end of its window. July 8th on a June 25th till July 15th window. Day 14 of a 21 day window. Spirit was day 3 of a 17 day window

Doug

I seem to recall that there was considerable pressure to get Oppy off on the night she actually launched -- the speculation was that if she didn't get off that night, she might not be able to launch at all. Perhaps there was a weather system approaching that made the last week of the launch window look iffy? All I recall for certain is that the press was speculating in a "now or never" vein...

-the other Doug

The cork didn't come off, since none was seen in the engine plumes. (Shedding launch vehicle debris is always is seen when it enters the plumes and is "lit up").

MERB was orginally on an Atlas II. But once the DII Heavy was available, it was found that it could meet the C3 requirements and the minimum 20 day launch period. This was a money saving measure, in that each the vehicle, integration and launch approval costs were cheaper. Integration and interfaces were identical and it ended up that the actual spacecraft were swapped because of a fuse problem. MER 2 flew on MER A launch and MER 1 flew on MER B launch.

So does anybody "really" know which rover is Spirit and which is Opportunity?

And hence why all Opportunitys images have a 1 serial number, and Spirits have 2

Doug

The Titan IIIE's were launched from the same pad, LC-41. The second vehicle was rolled to the pad and checked out and then moved to "storage", while the first vehicle was checked out and launched. Now the second vehicle could be sent back to the pad and launched. Any other LV would have required a second pad. The Titan ITL concept enabled one pad to be used. LC-40 was only configured to launch T-IIIC's

Actually, this was the only time these spacecraft could have been launched on Delta II's. Missing the 03 window would have sent the spacecraft to musuems, larger LV's would have been required in 05 and 07.

You are correct in that the EDL system contrained the total weight of the vehicle. So MER exceeding the capability of the Delta II during the minimum 20 day launch period was never an issue.

It wasn't quite that bad. But every day that MER A didn't launch, meant that MER B was delayed a day. There was a 10 day minimum interval between the missions. MERB couldn't be at the pad while MER A launched.

PS. Just a little info, I was the NASA LV integration engineer for both missions