NASA Probe Orbiting Asteroid Vesta

astroengine writes "Mission managers of NASA's Dawn asteroid probe had a long Saturday, waiting for news from the asteroid belt. Eventually they got the news they were hoping for: Dawn had entered Vesta orbit. This is the first time in history that an object in the asteroid belt has been orbited by an artificial satellite. It's taken four years for the ion thruster-propelled spacecraft to reach the asteroid and there was some uncertainty as to whether the probe had been captured by the asteroid's gravity at all. But after a long period of waiting, mission managers received the signal after Dawn was able to orientate its antenna toward Earth."

Re:Pics or it didn't happen.

[vlm]

When the ion drive isn't running, there is plenty of power. There's no reason to not gather as much data as possible. After all, if something went bung during insertion (when the probe was out of comms with Earth) it would be the only data they have. Given the detail in the last image (from ten days ago), what prevented them from at least getting a full surface sequence?

Other NASA probes take images from distant approach, trying to milk as much data as they can before the arrive, as well as PR for the mission. I can't find an explanation of why the Dawn team have been so reticent to image their target. It doesn't bode well for the rest of the mission.

I can think of a theoretical reason that may or may not have any application to reality.

We know the asteroid's orbit and our (the earths) orbit from a zillion years of position observation. We don't know the vehicle's relative velocity to the asteroid, and thats kind of important to put it in orbit. In ye olden days the stereotypical way to figure orbits was to put what amounts to a crossband linear repeater on the vehicle and spend inordinate amounts of effort on the earth measuring the doppler shift of signals transmitted thru the repeater. In ye olden days that was best done using an continuous information free carrier CW tone. Now a days the youngin's probably use some sort of spread spectrum solution to avoid ionospheric scintillation or just to plain ole be cool? At any rate the radios would probably be busy doing the navigation-thing as opposed to the science-thing.

Now a "news for nerds tech site" could make an interesting article about how this mission did navigation...

Re:What if they Pentagon bought more efficient A/C

[thrich81]

If it makes you feel any better, (it did for me) that number ($20 billion) for air conditioning in Afghanistan is highly debatable and was put forward by a guy who was a brigadier general but now is in the private sector, selling technologies branded as energy-efficient to the Defense Department. More from the source article (http://www.npr.org/2011/06/25/137414737/among-the-costs-of-war-20b-in-air-conditioning): "Now it's important to note that wrapped up in Anderson's $20 billion figure are all kind of other expenditures – for instance, the cost of building and maintaining roads in Afghanistan, securing those roads, managing the security operations for those roads. That all costs a lot of money and is part of the overall war effort in Afghanistan." And, "The Pentagon disputes the calculation made by Anderson about air conditioning costs. Defense Department spokesman Dave Lapan says that in fiscal year 2010, the Pentagon spent approximately $15 billion on energy for all military operations around the world. The Pentagon says when it comes to Afghanistan, it spent $1.5 billion from October 2010 to May 2011 on fuel. That fuel was used for heating and air conditioning systems, but also for aircraft, unmanned aerial systems, combat vehicles, computers and electricity inside military structures."

Re:Pics or it didn't happen.

[Anonymous Coward]

*sigh* So much misinformation floating around here...

GP said

That's because the only images they have are from the low-res navigational imager. They will fire up the high res camera and other instruments now that they're in Vesta orbit.

Which is absolute bullshit, because there's only one science camera (well, two identical cameras, for redundancy), and it's currently getting crap resolution because it's ~2x10^7m away, while science orbits will range from 2x10^6 to 2x10^5m altitude. There's also the star trackers, which while technically cameras, are not used for imaging Vesta or Ceres at all.

When the ion drive isn't running, there is plenty of power. There's no reason to not gather as much data as possible. After all, if something went bung during insertion (when the probe was out of comms with Earth) it would be the only data they have. Given the detail in the last image (from ten days ago), what prevented them from at least getting a full surface sequence?

Other NASA probes take images from distant approach, trying to milk as much data as they can before the arrive, as well as PR for the mission. I can't find an explanation of why the Dawn team have been so reticent to image their target. It doesn't bode well for the rest of the mission.

(It's not a power issue, it's an attitude issue -- each of the three ion thrusters is gimbaled in a narrow range, and the high-gain antenna and cameras are fixed completely -- same result, though.)
The mission's design duty cycle for the IPS (ion propulsion system) is 95%; the remaining 5% of the time is divided between imaging Vesta and relaying data to DSN ground stations. There's certainly time for more pics than they've taken, but allocating more time for imaging and less for thrusting means postponing your arrival, which reduces your time for doing high-quality science in orbit.

Unlike many other missions, which use a chemical rocket to perform a Hohmann or similar transfer into a near-final orbit, with relatively small deltaV reserved for orbit adjustments, Dawn will be gradually spiraling in under power to reach any given orbit. It's completely free to stop thrusting at any point and coast in a nearly-circular orbit while doing science observations, then resume spiraling in later, though they will likely stick to the mission plan of 3 orbits (2700km, 950km, and 460km radius -- subtract ~280km to get altitude). So there's very little to gain from more low-res approach images that we won't already get from the two full-rotation sets already scheduled (and I presume completed) during approach, and especially the full surface mapping that will be done in the first (highest) orbit. For more info on the navigation imaging strategy, see the latest Dawn Journal [nasa.gov].

The main issue is that they're not releasing the pictures they have -- particularly the full-rotation sets mentioned above, As I understand it this is mainly a manpower issue, but I certainly wish they could set up a low-overhead nerd-ready channel separate from their press-ready channel, so they could just dump all the images and let the bloggers sort 'em out.