Comments on: Dawn’s chief engineer reviews the mission

By: Edward

Edward — Mon, 07 Mar 2016 23:37:27 +0000

I see a great advantage to on-orbit manufacture and construction. There would still need to be verification that the fabrication was done right. For example, antennas and reflectors would need some form of anechoic chamber ( https://en.wikipedia.org/wiki/Anechoic_chamber ) to make sure that they broadcast and receive as they should.

There would also need to be an ability to fix or correct anything that did not work as it was expected to, which would allow for repairs of items that fail on orbit, perhaps extending their lifetimes and reducing insurance costs.

By: Steve Earle

Steve Earle — Mon, 07 Mar 2016 15:40:48 +0000

Interesting concepts. Another way to avoid high launch G’s would be a Space Plane. Not as gentle as an orbital tether but still better than a rocket launch.

Building on orbit would be the ideal. We need to start getting a lot more experience in space construction if we are ever to make the step past lab-experiments-for-show in a tinker toy space station…..

By: Tom Billings

Tom Billings — Sun, 06 Mar 2016 22:57:53 +0000

References for SpiderFab and Archinaut below:

http://spacenews.com/nasa-made-in-space-think-big-with-archinaut-a-robotic-3d-printing-demo-bound-for-iss/

http://www.tethers.com/SpiderFab.html

By: Tom Billings

Tom Billings — Sun, 06 Mar 2016 22:31:02 +0000

This mission is an excellent example of what directions future ion engine propulsion should go towards. First is using ion engines for attitude control, as is starting to be done for GEO comsats. This will save strongly on propellant mass taken up by Hydrazine in Dawn’s case. Second is making shorter missions, by increasing maximum thrust for inside gravity wells that must be climbed out of. A future ion engine mission should have the structure of the engine built in orbit, where its structure can be 1/10th as massive for the same thrust. This would be possible because the engine no longer has to survive 6 gees boost through the atmosphere, and worse acceleration by vibrations. For the same mass, it would allow 10 times the thrust, because a far larger structure for the engine will allow space-charge limitations of ion engines to be ameliorated through greater engine volume.

This will also make for lighter attitude control ion thrusters, that can placed farther from the center of mass, increasing their torque on the spacecraft, because they are built in orbit and added to the vehicle before it leaves. Finally, we should take advantage of these high volume thrusters by beaming power from either the Earth or from Earth orbit to the spacecraft as it leaves the gravity well. It has long been noted that the best returns for use of early and small solar power satellites are to power things *in*Space*, rather than competing with power sources already established here on Earth. This strategy will enable exits from the Earth/Moon gravity well at far higher rates, with less mission time and with a far higher percentage of the mass that current and near-term launchers can deliver to LEO devoted to the mission, instead of to climbing the gravity well. Once outside the Earth/Moon gravity well the option would be available to shed the engine mass that is not needed when the vehicle is only powered by its own solar cells, or its own nuke power plant.

Whether the scheme is the “Tethers Unlimited” concept of “SpiderFab”, or the “Made in Space” concept of “Archinaut”, or some other, matters less than that the building experience start being gathered ASAP.

By: Steve Earle

Steve Earle — Sun, 06 Mar 2016 17:00:42 +0000

Amazing mission. Growing up I was fascinated by Pioneer 10, and Voyagers 1 and 2. It’s incredible how well these and other spacecraft have performed above expectations.

Having said that, it appears that Dawn’s Ion engine is still working, too bad they can’t use that to put it into a Solar Orbit where it wouldn’t be necessary to use up the hydrazine remaining as quickly. Although the faulty reaction wheels would make that futile as well?

Just thinking out loud. Shame that the engine, electronics, and solar power are all in good shape otherwise….