**3.6 Micrometeoroids and Space Debris Issues:**

Description of the problem

Approaches to minimize the hazards of micrometeoroids and space debris

Protection against micrometeoroids and space debris during EVA

Impact emergency procedures

**MICROMETEOROIDS AND SPACE DEBRIS ISSUES**

This chapter is designed to provide you with a basic understanding of
micrometeoroids and space debris. Emphasis is placed on understanding
the problems posed by this space equivalent of "FOD" (Foreign Object
Damage") and the mitigation strategies currently in use.

![](media/image1.jpeg){width="2.997916666666667in"
height="2.9916666666666667in"}
![](media/image2.jpeg){width="2.8229166666666665in"
height="2.8229166666666665in"}

Figure 1: At left, space debris can be seen in the lower left of the
picture. The figure at right is an artist's image of the Earth showing
the currently tracked orbital debris in low earth orbit.
(http://eol.jsc.nasa.gov/sseop/images/ISD/lowres/STS088/STS088-724-68.JPG
and
http://www.orbitaldebris.jsc.nasa.gov/photogallery/photogallery.html)

**Description of the problem**

Spacecraft routinely collide with "space dust" 1 micron and larger.
Meteors (also known as meteroroids or micrometeoroids, depending upon
their size) are small bodies of solid matter moving through space that
originate in the interplanetary region, presumably from crumbling
asteroids or comets. Orbital debris, by contrast, is any man-made object
in orbit that no longer serves a useful purpose; a great deal of orbital
debris is material which comes from other spacecraft.

Most meteors (61%) are made of stone, with a sizable number (35%)
composed of iron. The vast majority of the micrometeoroid material is
\<0.1 mm in diameter. Although their size is tiny, they travel at such
high velocities that they have very great kinetic energy. When they
enter the Earth's atmosphere, they are heated by the friction of the
thickening air around them and may become visible as "shooting stars".
About 10 million kg of this interplanetary dust reaches the earth
surface every day and are then termed meteorites (or micrometeorites,
depending upon their size).

![](media/image3.jpeg){width="2.7083333333333335in"
height="2.051388888888889in"}![](media/image4.png){width="2.7506944444444446in"
height="1.6736111111111112in"}

Figure 2: Artist's rendition of a large meteor impacting Earth is shown
at left (http://mywebpages.comcast.net/cookewj/a_defense.html). Right,
an actual meteorite impact crater.
(http://www.dynamicearth.co.uk/education/howitallstarted_science.asp)

Since Sputnik was launched on October 4, 1957, nearly 30,000 other
objects have been put into orbit. \~9000 still remain in low earth orbit
(LEO), of which 94% fall into the category of "orbital debris".

![](media/image5.jpeg){width="4.250694444444444in"
height="2.954861111111111in"}

Figure 3: Sputnik (http://www.wbglinks.net/pages/history/)

Some estimates suggest that millions of kilograms are suspended in LEO,
of which the most numerous (42%) component is "fragmentation debris",
consisting of old satellite fragments (dead batteries, unused fuel
cells, etc) and deterioration products such as paint chips and aluminum
oxide particles left over from rocket fuel exhaust. Another 17% is
composed of rocket bodies, 22% of non-functional spacecraft, and the
final 19% is mission-related debris (tools dropped by EVA astronauts,
refuse, etc.). Orbital debris can remain in orbit indefinitely,
depending upon its orbital altitude. Objects at altitude \<200 km are
likely to fall to Earth within a few days, while those above 36,000 km
will stay in orbit forever[^1].

![](media/image6.jpeg){width="2.873611111111111in" height="2.24375in"}

Figure 4: Aluminum oxide debris from a solid rocket motor
(http://www.orbitaldebris.jsc.nasa.gov/photogallery/photogallery.html)

Collisions with either form of matter (micrometeoroids or orbital
debris, MMOD) take place at very rapid speeds (\~10km/s on average or 16
km/s for head on collisions), which obviously releases a great deal of
kinetic energy even for tiny objects such as paint flakes. As a result,
this material poses a danger to space travelers as well as to astronauts
in low earth orbit (LEO). For Shuttle missions, the risk of a lost
mission increases from 1/107 to 1/76 when MMOD is considered. MMOD was
termed the "number one loss of crew vehicle risk driver" in a 2003
probabilistic risk assessment (PRA), though the risk and consequence(s)
of the MMOD strike vary depending upon where on the orbiter the impact
occurs. In a September 2002 briefing, a senior ISS engineer reported
that MMOD was predicted to cause one ISS evacuation every 214 years.
This was considered the second most likely cause for an ISS evacuation,
with a medical emergency (including a radiation event) being the most
likely cause (estimated at 1 evacuation every 5 years). In the same
presentation, data was presented assuming a 40% chance of an MMOD-caused
hole in the ISS (over a 15 year lifespan of the station), with a 12.8%
chance (1 in 8) of the resultant hole necessitating a crew evacuation.

The longer a spacecraft is in orbit, the greater the risk of being
struck by some form of space matter. The number of micrometeoroids is
fairly constant in interplanetary space (for example during flights
between the Earth and Mars), but the gravitational forces near a planet
(i.e. in LEO) alter density patterns and trajectories. In addition,
orbital debris is naturally more plentiful in frequently used orbits, as
there have been more opportunities for debris to come off of spacecraft
in those areas. As a result, orbital debris varies with altitude and
inclination, and NASA is currently able to estimate the probability of
an impact with an object for a given orbit.

![](media/image7.jpeg){width="2.5527777777777776in"
height="2.5618055555555554in"}

Figure 5: Mir space station, which was in orbit from 1986-2001.
(http://physics.uwb.edu.pl/ptf/echa/encyklopedia/woronko/mir.jpg)

**Approaches to minimize the hazards of micrometeoroids and space
debris**

Very large objects (\>10-20 cm diameter) will usually be detected in
time to maneuver out of their way, while very small ones (\<0.1 cm
diameter) can be handled by current spacecraft shielding[^2].
Accordingly, there remains only a small number which are too big to be
controlled by shielding but still too tiny to detect before impact.
According to the NASA-JSC Office of Orbital Debris, "debris objects
smaller than 0.1 cm generally do not penetrate spacecraft \[but\] 0.1 --
1.0 cm debris penetrate and damage spacecraft \[while\] 1 cm debris
objects and larger will cause catastrophic failure (loss of
functionality of satellite due to impact)."

![](media/image8.jpeg){width="2.123611111111111in"
height="1.9409722222222223in"}
![](media/image9.jpeg){width="1.3888888888888888in" height="2.09375in"}
![](media/image10.jpeg){width="2.3756944444444446in"
height="1.8833333333333333in"}

Figure 6: Tracking stations in Alaska (left), California, and
Massachusetts (right) help to monitor the orbital position of thousands
of objects.
(http://www.orbitaldebris.jsc.nasa.gov/photogallery/photogallery.html)

In addition, during the inflight phase of its mission, the Shuttle is
oriented so that as it flies around the earth, the bulk of the vehicle
can protect more fragile equipment and astronauts during spacewalks from
impact.

Objects [\>]{.underline}1 cm in diameter can penetrate typical
spacecraft shielding, potentially causing depressurization of a
habitation module. The speed of such a depressurization will depend upon
the module volume and the size of the hole caused by the debris.

One way to mitigate the risk of depress due to an impact is to add more
shielding, but this increases spacecraft mass, requiring more lift to
get into orbit and to maneuver once there. Other mitigation strategies
include avoiding popular orbits, where there is more orbital debris, and
orienting sensitive surfaces (such as solar arrays) away from the
direction of travel in order to minimize the effects of an impact.

Efforts to reduce the threat posed by orbital debris are underway.
Currently, crews make every effort to limit the creation of orbital
debris. Newer satellites are designed to avoid breakup (a more common
occurrence in early models) and at the end of their lifespan they are
now placed in lower altitudes which will decay and permit destruction
during reentry. All NASA flight projects are now required to provide
debris assessments as part of the routine project development, and
debris tracking continues.

![](media/image11.png){width="3.623611111111111in"
height="2.765972222222222in"}

Figure 7: Artist's rendition of a satellite breaking apart.
(http://www.orbitaldebris.jsc.nasa.gov/photogallery/photogallery.html)

**Protection against micrometeoroids and space debris during EVA**

While spacecraft walls are thick enough to protect astronauts from
impacts with most of the tiny material out there, the risk to the crew
increases when they leave the shielded spacecraft, as during an
spacewalk ("extra-vehicular activity" or "EVA"). Spacesuits are designed
with a layer of shielding to protect the astronauts to the greatest
extent possible. However, even with this shielding, particles of
diameter [\>]{.underline}1mm may still be able to penetrate the outer
protective layer of the spacesuit, increasing the risk by an order of
magnitude (intravehicular astronauts generally only worry about objects
larger than 1 cm, while EVA astronauts are at risk from objects larger
than 1 mm).

![](media/image12.jpeg){width="4.125in" height="2.729861111111111in"}

Figure 8: Spacesuits for EVA have added layers to provide protection
against MMOD. Here, astronaut Don Pettit, Expedition Six ISS science
officer, assists colleague John Herrington, STS-113 mission specialist,
as he gets into his spacesuit in the Quest Airlock on the ISS.
(http://spaceflight.nasa.gov/gallery/images/shuttle/sts-113/html/sts113-340-029.html)

In addition to using layers of material in the space suits to protect
against MMOD, EVA astronauts are also safeguarded by limiting exposure
through short duration of EVAs and by planning EVAs at times and
locations outside of high risk orbits. Lunar and Martian EVAs will be
less dangerous than LEO, since these other bodies do not have orbital
debris. Of course, they will have "dust" from the surface, which is
likely to have an abrasive effect. Apollo crewmembers found that the
moon dust (actually a coarse grit) scratched their suits and visors, as
well as contaminated seals and bearings. Equipment was also damaged by
it. The electrostatic and mechanical properties made the dust cling to
the suit, causing problems in removing it before reentering the habitat.
Although Martian dust is likely to be more fine than moon dust (more
"talcum powder"-like) and therefore less abrasive, the contamination
issue will likely remain.

![](media/image13.jpeg){width="2.625in" height="1.9673611111111111in"}

Figure 9: Martian surface -- the dust here appears less coarse than moon
dust. (http://photojournal.jpl.nasa.gov/browse/PIA00608.jpg)

**Impact emergency procedures**

An example of an MMOD impact occurred on STS-94, when an impact crater
in one of the orbiter's windows was found after landing. The crater was
\~1mm diameter, and the MMOD object was estimated to be \~100 microns
(0.01cm) in size. Tests indicated that it was some aluminum oxide
residue from a solid rocket motor.

![](media/image14.jpeg){width="2.6875in" height="3.029861111111111in"}

Figure 10: An MMOD impact on the orbiter window during mission STS-7.
(http://www.orbitaldebris.jsc.nasa.gov/photogallery/photogallery.html)

Another example, this time of an unmanned satellite, occurred in 1996,
when a briefcase-sized piece of an Ariane 1 rocket body collided with a
Cerise communication satellite at 14 km/s (31,500 mph), severing the
satellite's 6 meter stabilization boom.

![](media/image15.jpeg){width="2.6875in" height="1.8118055555555554in"}
![](media/image16.jpeg){width="2.6875in" height="2.0729166666666665in"}

Figure 11: At left, an MMOD impact went completely through the Hubble
Space Telescope (HST) antenna dish. At right, the closeup shot shows
another MMOD strike on the HST.
(http://www.orbitaldebris.jsc.nasa.gov/measure/surfaceexam.html)

Impact emergency procedures vary considerably, depending upon the
situation. In the event of an unmanned spacecraft like the Cerise
satellite, the ground-based flight control team was able to reprogram
the on-board computer to correct the attitude despite the loss of the
stabilizer. If this had not been possible, the orbiter might have been
used to recover the satellite and return it to Earth for repairs, or it
might have entered such an unstable, tumbling configuration that it
would have been lost forever -- becoming part of the orbital debris
problem.

In the case of manned spacecraft, the worst case scenario would be that
of an astronaut on EVA whose spacesuit is struck and punctured by MMOD.
Again, procedures will depend upon where the impact is located. If the
MMOD strike is through the helmet, the impact may cause a nonsurvivable
injury. If it is on a more distal part of the body, it might be possible
to introduce a temporary patch and reenter the airlock before hypoxia
and incapacitation. Similarly, if a pressurized module, rather than a
space suit, is struck, the size and rate of the depressurization may
control the emergency procedures taken.

Following the Mir/Progress collision in 1997, when a Spektr module was
punctured and lost its pressure, the crew were able to safely evacuate
in a controlled fashion, because the leak was relatively slow. The
Spektr module was sealed off, and although it eventually dropped its
internal pressure to vacuum, the rest of the station never dropped below
675 mm Hg (normal: 750 mm Hg).

![](media/image17.jpeg){width="2.6034722222222224in" height="1.71875in"}

Figure 12: Mike Foale with Russian cosmonauts Pavel Vinogradov and
Anatoly Solovyev inside Mir in 1998. Vinogradov and Solovyev replaced
the Russian crew who experienced the depressurization with Foale.
(http://spaceflightnow.com/news/n0010/12lifeinspace/foale.jpg)

The following is Mike Foale's first person account of the Spektr
depressurization:

The Progress weighs seven tons. We think it collided at about three
meters a second. I was in the base block; I didn\'t see it at all. Sasha
Lazutkin saw it; he told me, in all haste, to go straight to the Soyuz
escape craft, and as I was passing into the node region of the Mir, I
heard a big thump. Because I wasn\'t touching the Mir, I didn\'t feel
any shock. I was just lightly floating through the node with my fingers
on it, about ten seconds after the warning. And there was this big kind
of ker-thump. And I assumed the Progress had hit back on the docking
port, where it was meant to have stuck.

But it hadn\'t. It had hit the Spektr module. If we\'d been strapped in,
we\'d have all been shaken around. This is just the opposite of being on
Earth, where you\'re in a car and you\'re always supposed to strap in.
Bash the space station, and nothing happens to you because you\'re not
in contact with the station \-- an interesting backwards twist.

...When we had the collision, we had a depressurization. The air rushed
out. Sasha and I, in about five minutes, had had to disconnect cables.
Some were powered and they sparked as we were cutting them; we quit
cutting and disconnected them manually. These were plugs about the size
of your hand. We got that cap in place in about ten minutes, it turned
out. We had about 20 minutes before we had to leave the station because
the air was too thin for us to breathe...

The station was hit very hard by the Progress. The guidance control
system that uses momentum wheels \-- gyrodynes, as they\'re called \--
to spin and then, in reaction, control the orientation of the station,
lost control. They couldn\'t handle that kind of knock. The whole
guidance control system failed in the station, at which point the
station started to tumble in an arbitrary way, about one degree a
second. These solar arrays are always supposed to be pointing to the
sun. And of course they can\'t slowly rotate about their axis to track
the sun. We rapidly \-- after the collision, in about three hours \--
started to lose all power.

So the station was totally quiet at night, and only woke up sometimes
during the day, when by chance some light would fall on this solar
array. And my task was to help Vasily and Sasha, who didn\'t know what
to do in this particular case, figure out what the orientation of the
station was by looking out through a window, to somehow stop the
rotation of the Soyuz. And then, knowing where the sun would be next
orbit, try to reorient the station so that the arrays were in an
orientation perpendicular to the sun. The next problem was to maintain
the orientation by putting a spin on the station \-- again firing
thrusters out of the Soyuz.

But this was with a station that had no power on it and with a Soyuz
that\'s not designed for moving stations around. If we had tried to
rotate the station, we\'d have used up almost all of the return fuel on
the Soyuz, and we would have been unable to abandon the station if we
were unsuccessful in doing this.

That was the jam we were in. This evolved over about thirty hours, with
us running from one window to the next, trying to figure out what the
orientation of the station was, and then looking at the stars \-- you\'d
put your thumb up against the window, watching the star move behind your
thumb. I know my thumb basically obscures \-- at least my thumb, anyway
\-- about three moon-widths; that\'s about one and a half degrees,
outstretched. And so I could very roughly and quickly, in a dark,
totally powered-down station, figure out what the angular rotation rates
of the station were. Then I told Vasily what I thought he should do in
the Soyuz.

But here comes the trick: to get from the part of the station where I
was doing the measurements to the Soyuz, you have to go through a node.
The node is basically a six-faced cube, just like a die, and it has
portholes in each direction. The trouble is, as you go through, you have
to go past these hatches, and you twist; and the Soyuz was not actually
lined up with the station, there are 45 degrees. So we spent almost a
whole orbit trying to work out what the orientation of the Soyuz was in
relation to the station \-- and we had no communication with the ground
to help us, because we had no power.

We were successful; we stabilized the station, at which point Sasha
Lazutkin and I tied it up to the central node area, so that we could
receive one of these docking adapter caps and put it in place of the cap
that we had put on the hole of the Spektr module to keep the air from
rushing out...

After that event, a new crew came up to replace Sasha and Vasily. By
that time, the ground and the Russians thought that the crew I was with,
the Mir-23 crew, were jinxed. A number of things had gone wrong in
between this slide and the last one; Sasha had gotten too tired one time
and pulled a cable while trying to reconfigure the inside of that node,
and again caused a total power-down of the station. But it was with some
regret and sadness that I saw that crew leave in the Soyuz spacecraft.

There\'s a suit inside the Soyuz called the Orlan. It\'s different from
the U.S. spacesuit in that it has a door at the back, and it opens up,
and you can step into it and then close it up behind you. You can
actually put the suit on all by itself; it\'s rather a neat design. The
next crew that came up \-- Anatoly Solovyev and Pavel Vinogradov \-- had
the task of entering into the Spektr module in vacuum \-- in spacesuits
\-- and reestablishing power from that module \-- and from the broken
solar arrays \-- to the rest of the station. While they were doing this
EVA into the Spektr module, I was inside the Soyuz spacecraft \-- just
in case those guys had a problem and couldn\'t repressurize the node and
get back into the station.

If that had been the case, I would have had to either try to get them
back into the spacecraft \-- putting air into the volume here where they
might enter \-- or leave them basically dead on the station. That EVA
went on for about six hours, and Pavel managed to make up most of the
power from the Spektr module back to the rest of the station, which
provided lifeblood for the station to recover. That repair work is what
this station is living on today."

Obviously the ISS has different emergency procedures than did the Mir,
and the protocols for exploration class missions will be different
still. The key in all of them, however, is evacuation of the crew to a
safe environment (along with removal of any critical supplies from the
affected area(s), should the circumstances permit), sealing off of the
affected area, and, when appropriate, repair and repressurization. Some
areas of the ISS can be safely sealed off -- the US lab module, for
example[^3] -- whereas others, such as the service module, would require
evacuation of the station, since the systems contained therein
(navigation, waste control, galley, etc) are required for the continued
function of the station and crew.

![](media/image18.jpeg){width="5.030555555555556in"
height="3.4166666666666665in"}

Figure 13: ISS -- the service module is at top left, where the grey
Soyuz capsule is docked ; the lab module is at bottom right.
(<http://www.space-adventures.de/archive-spaceflights.htm>)

**References and Suggested Readings**

1\) DeHart, RL and Davis, JR. (Eds.). (2002). [Fundamentals of Aerospace
Medicine, 3^rd^ Edition.]{.underline} Philadelphia: Lippincott Williams
& Wilkins.

2\) Larson WJ and Pranke LK (Eds.). (1999). [Human Spaceflight: Mission
Analysis and Design.]{.underline} New York: McGraw Hill.

3\) "Current Space Shuttle PRA Results", a PowerPoint presentation by
Bill Vesely, September 5, 2003,
http://atc.grc.nasa.gov/hostedEvents/rmc4/presentations/Day%201%209-4-03/6%20am%20Vesely.ppt#280,20,Slide
20

4\) Harding, R. (1989). [Survival in Space.]{.underline} London:
Routlege.

Office.

5\) "ISS Crew Return Capability: What Is the Risk?", a PowerPoint
presentation by Frank Buzzard, Senior System Integration Manager for
ISS, September 18, 2002,
http://risk.arc.nasa.gov/rmc3/downloads/day3/DAY3_AM/CRV%20Risk%209-023.ppt#291,7,Potential
for ISS Evacuation Due to Meteoroid/Debris Impact

6\) "Orbital Debris Education Package", NASA-JSC Orbital Debris Program
Office, http://sn-callisto.jsc.nasa.gov/library/EducationPackage.pdf

7\) Stine GH. (1997). [Living in Space: A Handbook for Work and
Exploration Stations Beyond the Earth's Atmosphere.]{.underline} New
York: M. Evans and Company.

8\) NASA JSC Orbital Debris Website, www.orbitaldebris.jsc.nasa.gov

9\) "What is Space Trash?",
http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question22.html

10\) "FOD News", http://www.fodnews.com/

11\) "Meteoroids and Orbital Debris: Effects on Spacecraft",
NASA/RP-1408, http://trs.nis.nasa.gov/archive/00000391/

12\) "NASA Orbital Debris Frequently Asked Questions",
http://sn-callisto.jsc.nasa.gov/faqs.html

13\) [*Interagency Report on Orbital
Debris*](http://sn-callisto.jsc.nasa.gov/library/IAR_95_Document.pdf)
(Office of Science and Technology Policy, Executive Office of the
President, 1995).

14\) United Nations *Technical Report on Space Debris*, New York, 1999.

15\) *Orbital Debris: A Technical Assessment* (National Research
Council, 1995).

16\) "Navigating on Mir: Michael Foale's keynote address at the 10^th^
anniversary *Mathematica* conference", June 19, 1998,
http://www.mathematica-journal.com/issue/v7i3/special/transcript/html/

17\) "Mir Space Station", http://www.russianspaceweb.com/mir.html

[^1]: Debris at an altitude of 200-600 km will likely stay in orbit
    several years, between 600-800 km, it will stay in orbit several
    decades, and at altitudes of 800-36,000 km it will remain there for
    centuries.

[^2]: The North American Aerospace Defense (NORAD) Command and United
    States Space Surveillance network tracks orbital debris \>10 cm in
    diameter so that spacecraft can maneuver around them; currently
    \~11,000 of these objects are being monitored. Another 100,000
    objects are estimated to fall in the 0.1-10 cm range and can neither
    be accurately tracked nor shielded against. The vast majority of
    orbital debris (numbering in the millions) are \<1 cm and are less
    likely to cause damage to a spacecraft.

[^3]: If the lab module were to depressurize and require evacuation by
    the crew, the astronauts have been told to remove as much of the
    American crew medical system as they safely can, prior to sealing
    the module. The Crew Health Care System (CHeCS) is located in the
    lab, and loss of those resources could be problematic, particularly
    if the crew sustained any injuries in the same event that caused the
    module depressurization.