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F.A.Q.
Lunar Prospector
Launch Vehicle
Scientists
Mission Control
Ames Research Center
Discovery Program
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Frequently Asked Questions
General information about Lunar Prospector
About the Moon
Specifics of the mission
Specifics of the instruments
What powers Prospector?
Lunar Prospector is run by rechargeable, solar-powered nickel-hydrogen
batteries.
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How big is Prospector?
The spacecraft is shaped like a drum, 4.25 feet (1.3 meters) -high,
with a diameter of 4.5 feet (1.4 meters). When full of fuel, Prospector
weighs 650 pounds (295 kilograms). The three masts are each 8 feet (2.4
meters) -long.
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What is unique about Prospector compared to
previous lunar missions?
The Apollo missions only mapped about 25 percent of the lunar surface,
around the Moon's equator. Prospector will map the entire lunar surface
for the first time. Additionally, Prospector will be much less expensive,
and carry fewer experiments, than the Apollo missions. It is NASA's third
Discovery mission and the first competitively selected Discovery mission.
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What will Prospector tell us?
Lunar Prospector will address many of the unanswered questions about
the Moon's resources, origin and structure that have been posed by NASA's
Lunar Exploration Science Working Group (LExSWG). This data could help
scientists plan a potential lunar base and develop theories of the formation
of the Moon, Earth and Solar System.
Prospector will determine whether
water ice exists on the Moon near its poles and map the elemental composition
of the lunar crust. It will detect outgassing (gas release from the lunar
interior) and study the relationship of outgassing to the lunar atmosphere.
It will map lunar magnetic fields, provide information about the Moon's
inner core, map the Moon's gravity field and investigate the effects of
volcanic activity and asteroid/comet impacts on the lunar surface.
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Will Lunar Prospector land on the Moon?
No. Prospector is an orbiter, not a lander, and will obtain all its
data remotely.
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How long will Prospector take to get to the
Moon?
Lunar Prospector's flight time to the Moon was 105 hours. It was launched
on January 6, 1998, and arrived at the Moon (entered lunar orbit) on January
11, 1998.
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Who built the spacecraft?
The spacecraft was built by Lockheed Martin Missiles & Space of
Sunnyvale, California.
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How old is the Moon?
Moon rock samples brought to Earth by the Apollo missions have been
dated to between 3 and 4.6 billion years old. The Earth is 4.5 to 4.6 billion
years old, but the oldest known Earth rocks are less than 4 billion years
old, and rocks older than 3 billion years are rare.
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How far is the Moon from the Earth?
On average, the Moon is 240,250 miles (384,400 km) from the Earth.
At the Moon's perigee (its closest approach to Earth in its elliptical
orbit), it is 227,063 miles (363,300 km) away. At its apogee (the farthest
distance away), the Moon is 253,438 miles (405,500 km) from the Earth.
It circles the Earth with a mean orbital velocity of 2,300 miles per hour
(3,680 km per hour).
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What are some of the physical differences
between the Earth and the Moon (size, mass)?
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Earth
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Moon
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| Mass (1024kg) |
5.9736
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0.07349
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| Volume(1010 km3) |
108.321
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2.1973
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| Mean radius(km) |
6371
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1737.5
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| Mean density(9 kg/m3) |
5520
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3340
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| Surface gravity(m/s2) |
9.78
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1.62
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| Escape velocity(km/s) |
11.2
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2.38
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Why do we only see one face of the Moon?
The Moon rotates once around its axis in the same amount of time it
completes a full orbit of the Earth. In other words, the Moon's rotational
period and its orbital period are equal. This is called synchronous rotation.
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Why are the Moon's magnetic fields so unique
(no dipole field)?
The Moon has no global magnetic field. But some of its surface rocks
exhibit remnant magnetism, indicating that there may have been a global
magnetic field early in the Moon's history. One of the questions Lunar
Prospector will address is whether an airless celestial body (like the
Moon) can acquire magnetic features from impacts, such as asteroids and
comets.
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Why is there no atmosphere on the Moon?
Basically, because it is too tiny. The Moon does not have a strong
enough gravitational field to support an atmosphere.
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What is a blue Moon?
A second full Moon in one month is called a blue Moon.
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How many times has NASA been to the Moon?
NASA has sent 22 missions to the Moon, between 1964 and 1972. NASA has
had six successful human landings on the Moon, preceded by two orbiters
with humans aboard.
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Why hasn't NASA been back to the Moon since
Apollo?
NASA funding decreased after the Apollo missions, and scientists wanted
to explore aspects of the Solar System other than the Moon.
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Why should we go back to the Moon now?
Much of the Moon remains a mystery. Data collected by the Apollo missions
focused on a narrow band around the Moon's equator, mapping only 25 percent
of the lunar surface. Prospector will fill in the gaps.
Scientists have been anxious to
return to the Moon since the Apollo missions, because prospecting for additional
information about the Moon's resources, composition, and gravitational
and magnetic fields is a necessary step toward planning future lunar missions,
particularly ones transporting humans. If a lunar base is established,
the Moon could become a stepping stone (or stop-off point) for missions
to the rest of the Solar System. Additionally, scientists are eager to
know the composition of the Moon because it will help them understand how
the Earth/Moon system evolved.
Now, we can explore the unknown
75 percent of the Moon's surface "Faster, Better, and Cheaper" with Lunar
Prospector.
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Why do we suspect there might be water on
the Moon?
Although we know that the Moon does not have any water of its own,
the Moon has been bombarded by comets -- mixtures of dust and ice -- for
billions of years. Any ice deposited on the lunar surface in the Moon's
thin atmosphere and bathed in warm sunlight would likely evaporate. However,
ice deposits would be unlikely to melt in very cold craters near the Moon's
south pole, where the Sun never shines. We expect, if we find water on
the Moon, that it will be frozen in soil deep in these craters.
The Department of Defense satellite,
Clementine, supported this suspicion with data it collected while flying
by the Moon in 1994. The Clementine data, though inconclusive, could be
explained by the presence of frozen water. Prospector will answer
this question.
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Why don't we already know about water on the
Moon?
Although the Apollo program returned vast amounts of lunar data to
Earth, those missions only studied equatorial regions of the Moon. Apollo
found no evidence of ice or water in those areas, and scientists suspect
that the Moon's surface is too warm near the equator to keep ice from evaporating
and exiting the thin atmosphere. However, deep, dark craters at the lunar
poles are very cold, and could be home to frozen water deposited by comets
over billions of years.
The Department of Defense satellite
Clementine studied the Moon when it flew by it in 1994, and transmitted
data about the Moon's polar craters back to Earth. Although Clementine's
results suggested that ice might be buried in craters near the Moon's south
pole, frozen water is only one possible explanation for Clementine's data.
Prospector will discover whether the water ice theory is correct.
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Why is finding water on the Moon significant?
The discovery of water ice on the Moon would be a vital step toward
the building of a human outpost on the Moon. According to NASA's February
1996 Strategic Plan, goals of NASA's Human Exploration and Development
of Space Enterprise (HEDS) include the following: "Explore and settle the
Solar System. Achieve routine space travel. Enrich life on Earth through
people living and working in space." In the Strategic Plan, HEDS indicates
the necessity for missions that will "demonstrate the feasibility of utilizing
local resources to 'live off the land,'" in order to meet its goals. Water
is an extremely expensive material to transport to the Moon. If Lunar Prospector
discovers water ice on the Moon, a very important local resource will be
available to astronauts because we use water to drink, to bathe and to
fuel spacecraft (after splitting water molecules into their individual
elemental components, hydrogen and oxygen).
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What does "spin-stabilized" mean?
The Lunar Prospector spacecraft rotates around its own up-and-down
axis, spinning like a top. Such "spin-stabilization" keeps the spacecraft's
orientation in space under control. Prospector's engineer's designed the
spacecraft to have a short and fat shape (as opposed to a long and narrow
one), so that an active damper isn't required to control wobbling.
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How was Prospector's launch date determined?
In planning a trip to the Moon, the two most important issues are power
and propellant. Lunar Prospector could have been launched to the Moon on
any day (in fact, two times a day -- see below), however only on those
days in which the spacecraft pointing and orbit insertion velocity constraints
are possible candidates. Firstly, to generate sufficient electrical power
to run the spacecraft, the solar array (solar panels) must be properly
pointed to "see" the Sun. Secondly, arrival at the Moon must correspond
to the time when the least amount of propellant is needed to fire the jets
and thus establish lunar orbit. Together, both of these constraints limit
the launch opportunity to only a few days each month.
Think of a trajectory to the Moon
as an oval with its perigee (closest point to Earth) at Cape Canaveral,
FL and its apogee (farthest point from Earth) at the Moon (upon arrival
in lunar orbit). The plane of that ellipse is fixed by the direcion of
launch -- due East from Florida. During each 24-hour day, Cape Canaveral
enters into that plane twice. Prospector could have been launched at either
of those times, which are 12 hours apart, but one was better able
to satisfy power and propellant constraints.
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What does the primary mission mean?
During its first year in orbit, Lunar Prospector will conduct its primary
mission. All five instruments will collect data as the spacecraft orbits
at an altitude of 63 miles (100 km) above the surface of the Moon.
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How will the spacecraft get to orbit (what
is the launch vehicle)?
The launch vehicle is a three-stage, solid fuel Lockheed Martin Athena
II rocket.
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What are you prospecting for? Are you looking
for gold and silver?
We are not prospecting for gold and silver. We are looking for resources
(such as water) in addition to certain elements (such as hydrogen, helium,
and iron) that would be very important to build and maintain a Solar System
"launchpad" and, perhaps, to eventually establish a lunar colony. Other
useful resources Lunar Prospector will search for are gases such as nitrogen
and carbon dioxide.
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Will you be bringing material back from the
Moon?
No. Prospector will orbit the Moon. Since the spacecraft will not land
on the Moon, and it will not return to Earth, it will not bring any lunar
samples back to Earth. It will, however, transmit vast amounts of data
to Earth before it impacts on the Moon's surface at the end of the mission.
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What will happen to Prospector after a year?
Prospector will begin an extended mission after its initial one-year
primary mission. During the extended period (after approximately another
six months), the mission will end when the spacecraft runs out of fuel.
It will then impact the surface of the Moon.
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What will the extended mission tell us?
After one year, we expect to have enough fuel left for Prospector to
drop down to an elliptical orbit with a minimum altitude of 6 miles (10
km). All five instruments will continue to function. The extended mission
will enable us to obtain data with much better resolution, since the spacecraft
will be in orbit longer, and Prospector will be closer to the surface.
Some of the instruments provide better data over a longer period of time,
and others do so at closer distances.
Because the Moon has an unusual,
non-uniform gravitational field, the spacecraft will not remain locked
in a stable, circular, polar orbit, as it would if the Moon were perfectly
round and the gravitational field did not vary. Therefore, Prospector will
be commanded to burn fuel to maintain its orbit, and we cannot predict
exactly how much fuel that will be. We do expect to have fuel for the extended
mission, possibly for six months after the primary mission ends. Once Prospector
has mapped the gravitational variances of the Moon, future lunar missions
will benefit economically because they will know more confidently how much
fuel to carry.
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What is required to achieve lunar orbit?
Lunar Prospector was launched from Pad 46 of Spaceport Florida (Cape
Canaveral, Florida) aboard a Lockheed Martin Athena II three-stage rocket.
As with all other space missions, the spacecraft was first launched into
a low Earth orbit, called a "parking orbit." After circling in this orbit
halfway around the Earth, the Trans Lunar Injection Stage (kick motor)
of the launch rocket fired, propelling Prospector toward the Moon. After
four days of coasting to the Moon, Prospector arrived at a distance 55
miles from the Moon. At that point, the spacecraft's thrusters (engines)
fired in order to slow the vehicle down and settle it into its final lunar
orbiting pattern, circling at 63 miles above the surface of the Moon.
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How fast will the spacecraft move around the
Moon?
Prospector will have an orbital velocity of 5,868 km per hour (3,668
miles per hour). It will circle the Moon once every 118 minutes.
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How far above the Moon does the spacecraft
orbit?
Prospector will map the Moon from a 63-mile (100-km) altitude orbit
during the one-year primary mission. If the spacecraft continues into an
extended mission (most likely for six months after the primary mission),
it will swing down to a 6-mile (10-km) altitude.
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How does the spacecraft get power when it
can't see the Sun?
A rechargeable battery will power Lunar Prospector while it is on the
dark side of the Moon. Each time it reappears in the Sun, it will recharge.
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What kind of computer runs the spacecraft?
There is no computer on board the spacecraft. A simple electronics
box, called the Command and Data Handling Unit, accepts a maximum of 60
commands from Earth. Lunar Prospector is controlled by a ground computer
at NASA Ames Research Center in Mountain View, California (San Franscisco
Bay Area).
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Will Lunar Prospector see the Apollo landing
sites?
Lunar Prospector will "see" the entire surface of the Moon. Although
the spacecraft does not carry a camera, it will conduct data measurements
over the entire lunar surface.
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Why will Prospector be in a polar orbit?
Lunar Prospector will be in a polar orbit because we want to map the
entire surface of the Moon. Prospector will circle the Moon, crossing both
the north and south poles, while the Moon spins on its north/south pole-axis.
As the spacecraft completes circle after circle, the Moon has rotated,
and all surfaces of the Moon will eventually be mapped.
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When and how will the data be transmitted
and received?
Lunar Prospector has two antennae, an omni antenna and a medium-gain
antenna. Both sit on top of the spacecraft (the omni sits above the medium-gain).
The omni antenna will be used for up-linking commands (en route to the
Moon), and the medium-gain antenna will be used while the spacecraft is
in lunar orbit, to down-link data to the Earth. An S-band transmitter and
an S-band receiver will communicate information between Prospector and
the Earth via NASA's Deep Space Network.
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What is outgassing (an outgassing event)?
Outgassing is the venting of gases from the lunar interior.
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What is a spectrometer?
A spectrometer is an instrument that detects incoming information (say,
light or matter) and disperses (scatters) it, organizing it according to
energy or mass. One kind of spectrometer is a prism -- it receives light
and spreads that light out into its individual wavelengths (which appear
as the colors of the rainbow).
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How will the masts deploy?
The booms deploy very much like springs unwinding. When mission controllers
provided the command to do so, a small device called a "pyrotechnic actuator"
ignited, melting a paraffin seal which released the booms to slowly unwind
in space.
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What is Discovery?
Discovery is NASA's new program for developing missions that return
the best science per dollar spent. The missions, which are by definition
"Faster, Better, and Cheaper," must follow strict, streamlined development
timelines and are required to adhere to a maximum budgetary constraint
of $150 million (1992 dollars) for development. Discovery encourages private
corporations, individuals and universities to work cooperatively with the
federal government. NASA issues an Announcement of Opportunity to call
for proposals from prospective mission designers.
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What are the booms (masts) for?
The booms isolate the instruments from the body of the spacecraft.
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Why doesn't Prospector have a camera?
Prospector can't do everything, and the Moon has already been extensively
photographed by previous missions. As a Discovery mission, Prospector has
a small payload of five instruments that focus on a narrow goal -- not
every experiment can be chosen. Non-Discovery missions carry multi-discipline
payloads of many more experiments, and consequently cost much more money.
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How will the mission end?
When Prospector's fuel runs out, scientists will not be able to make
orbital corrections and the spacecraft will impact the surface of the Moon.
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What did the mission cost?
Mission development cost about $34 million, which excludes the launch
vehicle (~$25 million) and the cost of operations (~$4 million). The total
cost was $63 million.
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What frequency will the spacecraft transmit
on?
The downlink frequency is 2273.000 MHz and the uplink frequency is
2093.0541 Mhz. Transmissions from the spacecraft to NASA's Deep Space Network
on Earth will be on the down-link frequency and commands to the spacecraft
from the Earth will be on the up-link frequency.
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