Tires on the ground ...

[Larry Burford] Some cruise missles use photographic landmark recognition for navagation. Do you think this would work for us, given the new high resolution satellite pictures? And the very slow speed of our vehicles.

MAF: I do not consider this to be practical for Mars. (a) The cruise missiles use photographic landmark resolution for terminal guidance, whereas, with the "shotgun" delivery approach proposed early in this topic, we won't know where any given rover is going to land with sufficient precision. In fact, I believe the biggest location problem is determination of approximate landing site, as I discuss in more detail below. (b) The cruise missile has a view angle somewhat close to the view from the satellite which acquired the reference images, whereas the rover camera, within ~1m of the Martian surface, does not. (c) The new cameras orbiting Mars can deliver sub-meter resolution, but most images are being acquired at lower resolutions, and it will be a *loooong* time before there is anything close to full-surface coverage at sub-meter resolution.
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[Larry Burford] The real limit is how far the rover can be allowed to travel in the 8 to 40 minutes of round-trip travel time for the control signals, and how often we can afford to update them.

MAF: Has anybody done a ballpark estimate of the uplink and downlink bandwidths that are going to be needed to control this fleet of rovers and to retrieve results therefrom? I would not be surprised if the calculation shows that an upgrade to Earth's interplanetary communication capacity will be required.
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[Larry Burford] If a rover pilot has a map (created from a hires photo) of the area near his rover, and the rover can image / lase / echo-range / <other sensor> the craters / hills / boulders / <other terrain features> in its vacintity, it ought to be possible for the pilot to mark a path around the obstacles, transmit that path to the rover, and the rover should be able to follow the path, perhaps with minor adjustments based on input from very short range sensor data to avoid small rocks, gullies, etc.

MAF: I agree in principle -- local navigation can be done based on high-resolution imagery and local sensor inputs. The hard part is going to be providing the rover pilot with the map. FIRST, it will be necessary to determine approximately where each rover has landed, which, absent a Mars-orbiting ranging platform, is decidedly non-trivial. IF the rovers' cameras were usable during descent, and IF the descending rovers had sufficient stability for the resulting images to be useful, it *might* be possible to estimate the landing positions with sufficient accuracy using the descent photos. Something that I consider to be more practical, and less expensive than the multiple orbiting ranging satellites that I suggested in an earlier post (although with longer position-determination times) is single-point triangulation from a single new data relay and ranging satellite in Martian polar orbit. I assume that *at least* one new data relay satellite is mandatory, as I cannot believe that there will be sufficient "spare" bandwidth through NASA's and ESA's existing and planned satellites to accommodate this fleet of rovers. SECOND, it will be necessary to create an accurate topographic map or DEM of each landing area. Unfortunately, it is *not* possible to do this using "a hires photo" because determination of topography requires *two* images, of equal resolution, proper angular overlap, and roughly equal sun angle (or one image and a georeferenced set of altimetry data, for which MOLA is inadequate, because its along-track resolution is only ~300m). Since I doubt that even one sub-meter image is likely to be on file for typical landing sites, I believe that some arrangement with NASA and/or ESA will be needed for acquisition of the necessary stereographic images after the landing site locations have been determined.
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[Larry Burford] BTW, do you see any tie-in with Stoat's idea? As I understand it, he is talking about a "map drawing" program that will create virtual roads that might (or might not) lead to/from areas of interest.

MAF: I find Stoat's path-generation idea to be very interesting. However, for it to be useful, you first need a sufficiently-accurate DEM of the relevant regions on Mars.

I suggest that we continue thinking about thse location, navigation, and communication issues in parallel with the more exciting subjects such as lander design and operation.

--Michael Fischer

When you find yourself on the side of the majority it is time to reform. -- Mark Twain

I looked up front wheel drive diffs for radio controlled racing cars and they are available at pretty cheap prices for nitro cars. We cut notches into the front steering wheels and pin through on the ball centre axle. I think we'll need to beef up the steering servo motor but steering left or right will shift the centre of mass of the central load and allow the ball to steer. The diff will stop any yaw forces on the central bar

Can we eject our rovers at a lower altitude? Say a hundered metres. Will that give us enough local air to inflate them? As I'm not keen on the idea of carrying gas bottles. Contamination being a worry.

Here is a proposal (though crudely drawn for a 360 spectrum launcher/CO2 generator for airbag landing. If these were stacked on a Delta Rocket they could be strewn over a large area of Mars and then each rover would make an overlapping pattern for discovery on the surface.



I know its a crude rendering, but I don't want to invest to heavily in an idea if it will be blown down by logic. Now, I know I might be jumping the gun, but I think the delivery system needs to be a major focus in figuring this out from a business standpoint. Thanks


Mark Vitrone

<b>[MAF] "Has anybody done a ballpark estimate of the uplink and downlink bandwidths that are going to be needed to control this fleet of rovers and to retrieve results therefrom? I would not be surprised if the calculation shows that an upgrade to Earth's interplanetary communication capacity will be required."</b>

Not yet. We need to define what info needs to flow, first. I suspect that the video data from the cameras will be 80% or more of the total Mars-to-Earth traffic.

Hmmm. Suppose that I'm close to right on this estimate. Video bandwidth for color TV is about 6 Mhz. If there are 100 rovers, the bandwidth needed is around 600/0.8 = 750 Mhz. For 1000 rovers, 7.5 Ghz. Doesn't sound too bad. Compression could be used to reduce this. But I suggest using the uncompressed figure for any design speculations you might do.

The Earth-to-Mars bandwith requirement is not likely to be as large.

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Mars-synchronus orbital radius = 20,900 km
Mars-synchronus orbital altitude = 17,400 km

This is close to GPS altitude here on Earth. Some cell phones have GPS functions built in. Does anyone know if they actually receive signals directly from the satellites? And the bandwidth of those signals?

Three synchronus satellites would give full time coverage from at least one satellite for all but the polar areas. Unfortunately, we need coverage of the polar areas. But maybe not at first?

LB

Some more <u>ball park</u> numbers for preliminary estimating:

Boosting a kilogram to LEO costs about $20,000. Rocket, gas, tracking, bribes, and so on. (For the Shuttle, but they usually aren't available. A Proton or an Ariane is likely to be (a little) cheaper and actually available. China or Japan may have some spare rockets, too.)

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Energy-wise (and therefore dollar-wise), LEO is roughly halfway to anywhere in the Solar System. So, $40,000 per kilo to Mars. (Ball park.)

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A one-kilo rover (including the pro-rata share of the mass of all the auxilliary stuff needed for safe delivery) is not impossible. But it isn't likely, either. 2 kilos per rover? 5?

We will need to be VERY creative.

And we also have to get our nav-comm system delivered.

LB

[Larry Burford] Suppose that I'm close to right on this estimate. Video bandwidth for color TV is about 6 Mhz. If there are 100 rovers, the bandwidth needed is around 600/0.8 = 750 Mhz. For 1000 rovers, 7.5 Ghz. Doesn't sound too bad. Compression could be used to reduce this. But I suggest using the uncompressed figure for any design speculations you might do.

MAF: This is not too bad for a fiber optic cable. Unfortunately, it is hard to string them between planets. For an interplanetary microwave link, with a few-watt transmitter at the far end, this is distinctly non-trivial. By way of comparison, 7.5Gb/s is about 3 orders of magnitude beyond the capability of today's Deep Space Network, which required an upgrade to support the MRO downlink that operates at 6Mb/s. The array-based Deep Space Network is intended to boost NASA's downlink capacity into the low-Gb/s range. This system, which will use 1200 12m antennas (400 at each of the 3 DSN sites) is currently in development, with full deployment projected for 2013(+). From a ballpark point of view, both compression, and greately-reduced resolution for navigation and survey activities seems appropriate. Detailed images can be transmitted over longer periods of time when necessary.
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[Larry Burford] The Earth-to-Mars bandwith requirement is not likely to be as large.

MAF: Agreed. With proper design, a few Mb/s should be adequate for the uplink. This ought to be possible, but still challenging, because the uplink has to be receivable and decodable using a single, small antenna on the relay satellite orbiting Mars.

--Michael Fischer


When you find yourself on the side of the majority it is time to reform. -- Mark Twain