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Dr. David Brain, Friday, 12-13-13 December 14, 2013

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Dr. David Brain, Friday, 12-13-13

http://archived.thespaceshow.com/shows/2142-BWB-2013-12-13.mp3

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Guest:  Dr. David Brain.  Topics: Mars MAVEN Mission, Mars science.  Please direct all comments and questions regarding Space Show programs/guest(s) to the Space Show blog, https://thespaceshow.wordpress.com.  Comments and questions should be relevant to the specific Space Show program. Written Transcripts of Space Show programs are a violation of our copyright and are not permitted without prior written consent, even if for your own use. We do not permit the commercial use of Space Show programs or any part thereof, nor do we permit editing, YouTube clips, or clips placed on other private channels & websites. Space Show programs can be quoted, but the quote must be cited or referenced using the proper citation format. Contact The Space Show for further information. In addition, please remember that your Amazon purchases can help support The Space Show/OGLF. See www.onegiantleapfoundation.org/amazon.htm.

We welcomed Dr. David Brain of the NASA MAVEN Mission team to the program for a discussion about MAVEN and Mars science.  In the first segment of our 1 hour 22 minute program, Dr. Brain provided us with an overview of the MAVEN Mission which was launched on Nov. 18.  As we heard, it is on track for its orbital insertion around Mars on Sept. 22, 2014.  I asked Dr. Brain if he thought Mars orbits were getting crowded and also if he knew if there were traffic management issues in orbiting Mars.  We also talked about the Indian Mars mission, Mangalyaan, as it was launched a few days before MAVEN and will arrive shortly after MAVEN arrives at Mars.  Dr. Brain, in describing MAVEN, said it was going to answer two questions:  1) What happened to the atmosphere of Mars and 2) What happened to the water and where did it go?  We then talked about the absence of a Martian magnetic field but we learned that there are strongly magnetized rocks along the edges and such rocks are 10-20 times the magnetic strength of similar rocks on Earth.  Dr. Brain provided us with theories on this.  We extrapolated that it was possible for something similar to happen on Earth.  He also talked about magnetic fields, how one might generate a magnetic field on Mars & more.  This latter point was in reply to a listener question asking if terraforming included creating a Martian magnetic field.  Our next topic dealt with how these types of missions are developed, the hardware and scientific tool risk issues, the use of heritage hardware and instruments, program funding, and review panels.  Marshall called and talked about instrument redundancy, electronic improvements from mission to mission and more.  We also talked about sending data back to Earth using the Deep Space Network (DSN).  This brought up questions about private Mars missions using the DSN for their communications.

In the second segment, Doug called to ask how MAVEN was impacted by the government shutdown. Dave relayed the shutdown stories to us which were most interesting, especially since it went right up to the minute for possible mission delays of 18-24 months.  In fact, MAVEN did get an exemption from the shutdown but not because of its science.  It was exempted because of its function as a communications relay satellite.  Also in this segment, Dave responded to listener questions asking how the instruments are designed, tested, and protected for their trip to Mars so they would be sure to work.  Dave took us through the entire process for planning, designing, developing and testing hardware & operating components  over and over again.    This is a fascinating inside look at what is involved in a successful Mars, lunar, or planetary mission.  Doug then asked about methane on Mars and here Dave had much to say about competing methane theories and the latest findings from instruments on Mars including Curiosity.

Please post your comments/questions on The Space Show blog above.  Dr. Brain can be contacted through me.

Comments»

1. rocketscirick - December 20, 2013

Seems we have hit this subtopic of DSN at an opportune time. Dec. 24, 2013, will mark “the 50th anniversary of its official creation.”
http://www.jpl.nasa.gov/news/news.php?release=2013-370

Earlier, I said “interplanetary relays in the vicinity of STEREO-A and -B.” What I had intended by that was Sun-Earth L4 and L5 points. I just checked, and those two spacecraft are now well beyond those points. While ideal for continuous communication, it strikes me as overly ambitious, and really long range, which I’m starting to detest.

To be somewhat more realistic, a single cluster around Earth-Moon L4 or L5 might make good sense. For each planet with an emerging spacecraft armada (Mars, Jupiter, Saturn; I know, I’m dreaming), there should be a combined laser/RF comm platform with that planet as its only target. Another laser/RF platform should point at Earth. And a spare might be used for certain en route spacecraft, and as back-up the planet-targeting platforms when one of them fails. Of course, the platforms would talk wirelessly at short range. (Note that when you are in space, you don’t have a big mass like the Earth to steer against. So a dedicated planetary target starts to make more sense.)

It is possible that TDRS might be outfitted with repeaters to improve the downlink to Earth. I’m under the impression that the current satellites’ antenna arrays only point toward Earth. I’m a little leery of putting the actual planetary comm platforms in geosync orbit due to signals having to periodically pass through the heavy band of other satellites in that zone, with possible crosstalk implications.

There are interesting issues of what you do with the Earth or Sun get in the way of line of sight to the planet, but I imagine we also have those problems today with the Moon and Sun.

Now, since I am not a real space comm guy, I don’t know how many engineering miracles I am asking for. (Long-term operation in a solar active environment, light-weight precision-pointing antenna, photovoltaic systems generating enough power for long range comm.) I wonder if someone at JPL has already proposed such a thing and would be willing to talk about it.

2. Dwayne Day - December 18, 2013

There was some discussion of the DSN. Several points:

LRO actually constructed its own ground stations separate from the DSN (and I presume other American missions to the Moon, such as GRAIL, used this too). The Moon is relatively easy and doesn’t require big dishes, so China, for instance, built their own dishes for communicating with Chang’e-3.

The DSN’s schedule is very full. Every new deep space mission has to come up with a plan for using the DSN. This is usually a back and forth negotiation with the DSN people. Essentially what happens is that the mission says “We want all this time” and then the DSN people say “You can have only a fraction of this time” and then they go back and forth negotiating based upon all the other missions using DSN (and that includes using the big Goldstone dish for radar imaging of asteroids and other targets). It is a complicated scheduling problem and suffice to say that nobody ever gets all the DSN time they want.

I think that Europe built their own ground stations for some of their spacecraft, and they probably have sharing agreements with NASA for the DSN. Keep in mind that different ground stations provide different capabilities and coverage. For instance, for deep space spacecraft (like New Horizons on its way to Pluto) you really need the big, old DSN dishes. And dishes break down too. So sometimes users get bumped. Having a good system for managing your data and communications is really important for a successful mission.

There have been numerous proposals for upgrading DSN over the years. Part of this is because of aging infrastructure (some of the breakdowns of the big dishes can require very expensive replacement parts). I have lost track of the current modernization plan, but the goal was to retire at least one or two of the big dishes and use smaller, more standardized dishes that are similar to those used for commercial purposes, saving on installation and repair costs.

LADEE has demonstrated laser comm from lunar orbit, and that is an important technology development that might prompt more such projects in the future, but the planetary program is currently suffering budget cuts and has little money for technology.

The ultimate DSN would use orbiting satellites, like TDRSS, equipped with laser receivers. There are some tough problems with this, however. First, pointing requirements for distant spacecraft (beyond Mars) are apparently really high, so you still might need standard dishes for them. Second, you’d still have to deal with clouds, so the laser signals would probably have to be converted to radio and then beamed down to Earth, and that is a tough processing challenge. Finally, this approach is expensive. It might eventually make sense to merge TDRSS and DSN missions to some extent in the future, but that is mixing missions and technical requirements (receiving from above vs. below, etc.) and might be something that could happen many decades from now.

Finally, I did hear a second-hand story about Tito’s Inspiration Mars people briefing some NASA group a number of months back and the IM people indicated that they wanted continuous hi-def video from their spacecraft during the entire mission. Apparently this emitted laughter from some of the NASA people. If that’s what IM wants, they should start building their own ground stations now, because NASA cannot stretch the DSN like that.

3. rocketscirick - December 15, 2013

The question of DSN capacity limits and alternatives has intrigued me for several years. Alas, I am not a DSN expert, but I had accidental access to one a few years ago. (I’ve tried a few times over the years to contact my expert again, but have been unsuccessful.)

I’d like to see an armada of spacecraft around each of the outer planets, with decent speed backbone of many, many megabits/second pointed at Earth.

For each planetary cluster of spacecraft or independent probes like STEREO-A and -B, or Voyager 1 and 2, there needs to be an antenna pointed at it at the right time. If you have more spacecraft than antennae, then you need to make sure that your particular spacecraft is not transmitting when no one is looking. (Throw in appropriate light distance measures for proper synchronization.) That is, the appropriate antenna on the correct side of the Earth needs to be pointed in the direction of the signal that is about to hit.

The Mars Explorations Rovers transmit from the surface to a relay like Mars Reconnaissance Orbiter (MRO) at 256K bits/second, or lower if MRO is just off the horizon. From the relay to Earth, it would then transmit at 128K bits/second. At that rate, if you have an color picture with red, green, and blue channels (assuming 8 bits/channel, thus, 24 bits/pixel), an uncompressed picture of 1024×1024 pixels would take 196 seconds to transmit to Earth. I believe there is some compression, but I couldn’t tell you how much, and efficiency probably depends on the complexity of the picture. (Pictures of the sky compress more easily than pictures of a complex rugged terrain.) MRO is able to transmit at 6 megabits/second. But I don’t know if it does this on a regular basis.

I just stumbled on a Cassini fact sheet from 1999 that puts its peak data rate at 249K bits/second. Considering its distance and age, to me that seems pretty impressive.

There was a Mars Telecommunications Orbiter planned at one time, which would have demonstrated the use of lasers from Mars for communication, and provide a major increase in bandwidth. However, in 2005, it was a victim of budget problems and canceled.

LADEE carries a laser comm experiment, and demonstrated 622 megabits/second. But a place on Earth is a very close target for it, and probably hard to miss. Transmitting from a distant planet would require pinpoint targeting for it to be useful. If you turn the spacecraft one way to collect data, and then another way to communicate, I can see this getting very time-consuming. This almost argues for a relay that has a laser always pointing at Earth. It can use conventional radio to communicate with other spacecraft in its planetary vicinity.

With the Earth rotating under a steered ground antenna, and attenuation when you dip lower into the atmosphere, it makes sense to me to have dedicated antennae in GEO or higher, always pointing at a planetary neighborhood, using laser to send and receive.

We could also use interplanetary relays in the vicinity of STEREO-A and -B. That way, when a planet is on the other side of the Sun from Earth, we would still have the capability of receiving data, and probably avoid a lot of radio noise from the Sun.

So there. You have my outline of an interplanetary relay system, on which you could layer elements of the InterPlanetary interNet (IPN, which is a related, but different subject). 🙂

–Rick in Silicon Valley


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