The Micro Meteoroid Mapping Mission idea.

[john smith 19]

There is a lot of concern over objects within 2000 Km of the Earth's surface and its potential for damage if it hits an orbiting satellite or LV during launch. The US Space Command seems to be able to track objects > 10cm fairly well. Beyond that the picture gets hazy. The issue seems to be that they do most of their tracking using ICBM warning radars. Their operating wavelength seems to be about 10cm, so anything smaller (and NASA reckons anything > 10mm (sugar cube sized) can cause significant damage, is simply invisible to them. They are also unlikely to be pointing upward, so they are operating on a very long "slant range".

Seeing these objects is the aim of the Micro Meteoroid Mapping Mission (M4).

By placing a satellite in polar orbit at around 500Km with 2 LIDAR sensors, one looking up, one down, with an effective range of 500Km (roughly to the bottom edge of the inner Van Allen belt upward, so covering the region most LEO sats fly through routinely) you should see all objects and ease the accuracy requirements.

Ideally M4 is a secondary payload launched into polar orbit. It scans a swath angle wide enough so there is some overlap between scans and precesses (IE not quite an integer # of orbits per day) so the blind spots (basically an elongated diamond shaped hole) are covered as well. It uses passive stabilization methods to keep it's bottom side looking down at the local vertical and top side looking up and gets all power from cells on its 1m cube sides (so no extendable solar panels).It has no thrusters for RCS or orbit changing and it's key active components can be switched and/or shared with the opposite channel to continue working with reduced capacity in the event of failure. It's design life should cover a bit more than 1 full solar cycle, EG 12-13 years.. Its data is as good as the US Space Command for larger objects. It can track objects down to 1mm in size. AFAP it uses COTS parts for both the electronics and the optics IE near IR components from the optical networking industry. Down link is by TDRSS.

IRL?.  The MOST space telescope showed you could do useful science in a 53Kg package and in a polar orbit and operated for 10 years,  so that order of life expectancy is possible. I'm not sure how easy that would be to repeat.

I'd hope to get at least (roughly) coverage from the launch site latitude to the equator (and on the other side of the equator as well). Likewise simultaneous coverage up and down. I think you could get conservatively 15W of laser light from the 2 channels. That's from 1 full face illuminated by AM0 sun with 21.6% efficient PV cells, roughly 1/2 the world record for space solar cells. The 15W laser power comes from dedicating 150W to the laser drives and assuming 10% laser efficiency. I hope people will correct my mistakes in these areas. That leaves about 100W for other systems.

I don't know if you could do 2 full channels or have to time slice between looking up or down, either of the transmitter, the receivers, or both.

I think this would make an interesting and useful mission for a variety of universities but in which case why has it not flown already?

So what have I missed? Would flying as a primary be cost effective? Is it feasible (but challenging) in 100Kg? Is 1mm wide object detection (that's roughly 900 wavelengths wide at a near IR wavelength) at 500Km reasonable?

A few numbers.
MOST's 820Km has a period of about 101minutes so 500Kms should be shorter but above Shuttles roughly 90mins.  At 101 minutes it completed about 14.25 orbits/day. 14 orbits gives a swath angle of 25.72deg, Anything over a 26deg scan angle (13deg from centreline) for M4 would give an overlap. MOST achieved 1 arc second pointing accuracy using 4 reaction wheels and mag torquers. The telescope was F/6 with a 15cm aperture in the long face of the box 0.65 x  0.65 x 0.3m volume. Reaction wheel failure ended the mission.

[kevin-rf]

Did you happen to glance through the thread on the Space Fence shutdown and the replacement being designed?

http://forum.nasaspaceflight.com/index.php?topic=32566.msg1107920

Especially the excellent in-depth article on the whole issue?
http://www.thespacereview.com/article/2357/1

The 10 cm detection limit was dictated by the 216.98 MHz signal used by the former AFSSS

The S-Band Space Fence replacement planned for the gap is at a higher frequency system that should detect smaller obects, if it ever gets funded.

Note while the USAF uses visible and radar methods for tracking space junk. The only satellite they have placed in orbit for this task (Space Based Space Surveillance (SBSS)) was IR. These kind of things just show up better in the IR.

[SWGlassPit]

A couple thoughts on this idea -- mostly nit-picky:

This satellite would be looking for orbital debris, not meteoroids.  Meteoroids are objects in a solar orbit and are not generally tracked, as they approach with closing velocities between 11 and 70 km/s (i.e., earth escape velocity at the slowest!) and are generally extremely small.

The orbital debris threat to any particular satellite is highly inclination dependent.  Any satellite-based detection system would need to determine what orbit any particular particle is in.  Particles in inclinations very close to the proposed mission's orbit would likely not be detected very frequently, especially if they are in orbits of similar altitude.  Being in a polar orbit, however, they would account for a large percentage of the threat to satellites in orbits of different inclinations.  A mission like this would ideally need multiple detection vehicles in grossly different orbits.

The wavelengths needed to detect particles small enough to pose a threat would present a lot of noise for a nadir-facing detector to discriminate against.  My expertise is not in sensors, so this may in fact be a non-issue, but it is something else to consider.

[john smith 19]

A couple thoughts on this idea -- mostly nit-picky:

This satellite would be looking for orbital debris, not meteoroids.  Meteoroids are objects in a solar orbit and are not generally tracked, as they approach with closing velocities between 11 and 70 km/s (i.e., earth escape velocity at the slowest!) and are generally extremely small.

Noted. I guess my working definition was (roughly) "Stuff that will do serious harm to a space payload or an astronaut if it hits them."

The orbital debris threat to any particular satellite is highly inclination dependent.  Any satellite-based detection system would need to determine what orbit any particular particle is in.  Particles in inclinations very close to the proposed mission's orbit would likely not be detected very frequently, especially if they are in orbits of similar altitude.  Being in a polar orbit, however, they would account for a large percentage of the threat to satellites in orbits of different inclinations.  A mission like this would ideally need multiple detection vehicles in grossly different orbits.

If I understand the problem you're describing that's the reason why the orbit would not be an integer multiple of the Earths period, so the orbit sweeps those "blind spots," while the off axis sweep would detect items flying "one above the other" so to speak. That said if the object was just behind the orbit when M4 started operating it would not be picked up until M4's orbit had precessed round, which looks like it could take weeks.

The concept is really more the sort of thing a university could do just to get an idea of what the scale of the problem is. But to do it full justice would probably take multiple launches, as the inclinations would be widely different in order to pick up items quickly.

The wavelengths needed to detect particles small enough to pose a threat would present a lot of noise for a nadir-facing detector to discriminate against.  My expertise is not in sensors, so this may in fact be a non-issue, but it is something else to consider.

Well I'd hope the laser energy would be far above background and the reflected energy (although very attenuated) would still be quite far above background.  But that's one of the questions about is this feasible.

Did you happen to glance through the thread on the Space Fence shutdown and the replacement being designed?

http://forum.nasaspaceflight.com/index.php?topic=32566.msg1107920

Especially the excellent in-depth article on the whole issue?
http://www.thespacereview.com/article/2357/1

Excellent article. Very Thorough.  Saving $16m??? That's the Pentagon office xmas party fund? As others pointed out that's not even the replacement cost of one satellite launched on a sponsored govt programme.   

The 10 cm detection limit was dictated by the 216.98 MHz signal used by the former AFSSS

The S-Band Space Fence replacement planned for the gap is at a higher frequency system that should detect smaller obects, if it ever gets funded.

That did surprise me. I'm used to seeing X band radars and so I assumed the limit was set for that.

Note that raising the frequency 10x only reduces the size detected by 2.

Note while the USAF uses visible and radar methods for tracking space junk. The only satellite they have placed in orbit for this task (Space Based Space Surveillance (SBSS)) was IR. These kind of things just show up better in the IR.

M4 is an active system, but it would also be in the IR range.

I got the impression SBSS was pretty expensive and had to keep being rescheduled?

[SWGlassPit]

Here's a list of papers on NTRS that talk about what we know to date about the orbital debris environment.

[kevin-rf]

If I understand the problem you're describing that's the reason why the orbit would not be an integer multiple of the Earths period, so the orbit sweeps those "blind spots," while the off axis sweep would detect items flying "one above the other" so to speak. That said if the object was just behind the orbit when M4 started operating it would not be picked up until M4's orbit had precessed round, which looks like it could take weeks.

The concept is really more the sort of thing a university could do just to get an idea of what the scale of the problem is. But to do it full justice would probably take multiple launches, as the inclinations would be widely different in order to pick up items quickly.

You are better off with an equatorial orbit, all orbit's cross that plane twice an orbit. You will only get two types of misses.

1. Orbit's that are in some sort of resonance with the orbit, so they get missed. Less likely with a low inclination orbit.
2. Extremely eccentric orbits that have apogees that fall outside of the detection range and have perigee over the poles. Stuff in Molniya type orbits will be missed.

Also, if you orbit low enough you do not need to look down, the drag in LEO will quickly clean the space anyway. Just pick a compromise orbit where the drag is low enough that only periodic re boost is needed.

Why only look straight up and down, you scan more volume if you look sideways.

[kevin-rf]

SBSS was not that large of a satellite, wiki has the program costing $823 million. Not cheap, that includes everything, satellite, launch, ground stations.

http://en.wikipedia.org/wiki/SBSS

I thought I read that a follow on had been canceled due to budget pressures.

[john smith 19]

SBSS was not that large of a satellite, wiki has the program costing $823 million. Not cheap, that includes everything, satellite, launch, ground stations.

http://en.wikipedia.org/wiki/SBSS

I thought I read that a follow on had been canceled due to budget pressures.

I'm pretty sure I saw an article in the Space Review on it that was fairly critical. IIRC they were planning multiple satellites to give the necessary coverage

You are better off with an equatorial orbit, all orbit's cross that plane twice an orbit. You will only get two types of misses.

1. Orbit's that are in some sort of resonance with the orbit, so they get missed. Less likely with a low inclination orbit.
2. Extremely eccentric orbits that have apogees that fall outside of the detection range and have perigee over the poles. Stuff in Molniya type orbits will be missed.

True. But part of this would be to get a feel for debris over the whole Earth. For example do multiple debris fields or orbits intersect to create an orbital "bear pit" that virtually guarantees damage?

If the funding were available I'm wondering if 2 satellites (orbital and equatorial) would give most of the coverage needed.

Also, if you orbit low enough you do not need to look down, the drag in LEO will quickly clean the space anyway. Just pick a compromise orbit where the drag is low enough that only periodic re boost is needed.

Why only look straight up and down, you scan more volume if you look sideways.

With a satellite midway between Earth and the bottom of the lower Van Allan belt you halve the range needed for each channel, but just as importantly you should have higher range accuracy because of that halved range. You also don't need (AFAIK) a re-boost, which if you want a long life certainly helps, give propellant depletion is a major EoL mode for sats.

Volume wise the Earth is the gravity well in NEO. Note that in my mission idea the beams do not literally point up and down but would have enough fan out to pick up most of what's between them as the ground track precesses under the satellite.

Interesting list. Could you explain how you got it?

[SWGlassPit]

Interesting list. Could you explain how you got it?

It's just a search on NTRS for the name of the current orbital debris model used by NASA.

[kevin-rf]

The thread would not be complete without a link to this:

http://orbitaldebris.jsc.nasa.gov/newsletter/newsletter.html

[john smith 19]

The thread would not be complete without a link to this:

http://orbitaldebris.jsc.nasa.gov/newsletter/newsletter.html

True. It should be on everyone's reading list if they are interested in this subject.

[john smith 19]

A polar orbit was my best guess at an orbit to cover all part of the Earth to get a feel for the debris problem.

I'd also be interested in how feasible people think a dual LIDAR system with a 500Km range and resolution to 1mm is