LAMO, aka Low Altitude Mapping Orbit Options

[dilo]

I think is time to start this new topic, now that Dawn is more than half-way in the transition from HAMO to LAMO (as showed in the plot below).

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[Explorer1]

Yeah, Dawn's launch was delayed three months, but the ion drive gives so much leeway it didn't matter in the end (compared with a conventional launch to Mars for example, that has a very specific window).

[Greg Hullender]

Yeah, Dawn's launch was delayed three months, but the ion drive gives so much leeway it didn't matter in the end (compared with a conventional launch to Mars for example, that has a very specific window).

Supposedly that delay was running up against the window from Vesta to Ceres, so I suspect there may not be much more leeway to stay at Vesta. Perhaps someone who knows for sure will chime in.

--Greg

[Greg Hullender]

Supposedly that delay was running up against the window from Vesta to Ceres, so I suspect there may not be much more leeway to stay at Vesta. Perhaps someone who knows for sure will chime in.

--Greg

Sure enough, I got the following from Marc Rayman, which he invited me to share here:

We have quite a bit of technical flexibility to shift the Vesta departure. You're correct that we launched relatively late in the multiyear launch period for reaching both Vesta and Ceres, but that does not impose a significant constraint now. You may recall that our prelaunch model for the solar array power as a function of heliocentric range was demonstrated in flight to be conservative. Thanks to the ion propulsion system, we translated that power margin into the more operationally and scientifically useful resource of residence time at Vesta. But there has always been another constraint, and that is funding. Our mission timeline includes reaching Ceres in February 2015 not for reasons of celestial mechanics but because that is the schedule upon which the budget was formulated. The celestial mechanics is such that the time to travel from Vesta to Ceres is pretty insensitive to the departure date for up to ~ 0.5 years later than July 2012. But leaving later would mean an extension to the primary mission, and that is not budgeted. The simple reality, which I know you recognize, is that funding is extremely (perhaps even uniquely) tight these days.

As soon as we determined the Vesta pole during the approach phase, we knew what it meant for seeing the north pole, but our plan to depart in July 2012 has not changed. Our agreement with NASA HQ (formalized in our level 1 requirements) has always been that we would image at least 80% of the surface of Vesta at 100 m/px in our panchromatic channel and at least three color filters. We have already done better than that, so it is not obvious that we have to see farther north, much as one might consider it to be neat to do so.

In case this appears to be inconsistent with Emily's tweet about what Chris Russell said here at the AGU, let me be be explicit about it. It is correct that we would need to delay departure in order to see all the way to the north pole. That is not the same as saying we will delay departure.

While plans may change, we remain scheduled for departure in July. We already have fabulous data on Vesta, and we certainly will have even more by then. It certainly would be nice to see the entire surface, but even if we don't, there's no doubt that what we will have seen at Vesta will be exceptionally valuable.

Hope everyone has a happy (and interesting) New Year!

--Greg