ASTR 330: The Solar System
Announcements
• Homework #6 due Tuesday, December 12th.
• Extra-credit papers will also be returned on Tuesday.
• This is the last regular class: Tuesday’s class will be a fun
(!) team working game.
• This lecture will summarize some aspects of spacecraft
mission which will be useful on Tuesday!
• On-line evaluation:
https://www.courses.umd.edu/online_evaluation/
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Space Mission Game!
• Tuesdays class will take the form of a team working game.
• The purpose is to emulate the process which occurs in
NASA, of proposing, promoting and finally selecting a
space mission to fund and develop, from competing
proposals.
•
The Space Mission Game will build on Homework #6, so
make sure you have completed it ahead of time!
• You may also want to bring some extra copies of your
homework with you to distribute to team members.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Space Mission Game!
• The class will be divided into groups of 6-7, in teams. Each
team will be required to:
1. Select, from amongst your homework #6 assignments, one
mission plan to present to the class. You may meld
elements from several proposals into a new proposal.
2. Prepare a presentation to the class. At least two team
members must present. Presentations should take about 3
minutes or less.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Presentations
• The presentation will take the following form:
1. TITLE - giving mission name, logo, graphic, team
member names.
2. SCIENCE OBJECTIVES - list no more than three
principal science objectives. Say why each is important.
3. TECHNICAL PLAN - brief description of mission, and
spacecraft especially instruments (max 5). Sketch.
4. SUMMARY - convince the judging panel.
• Presentation materials (pens, transparencies) will be
provided. You will have about 40 minutes to prepare.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Judging and Scoring
• One member from each team will volunteer to join a
judging panel at the start of the class.
• The judging panel will devise a scoring rubric and then
assess each proposal in turn. At the end, they must select
one mission to fund!
• All students who participate will receive 10 extra credit
course points.
• The team which receives the highest score will also receive
5 bonus extra credit course points.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Exams
• Final exam: Tuesday December 19th, 1:30-3:30 pm.
Room CSS 2428.
• Final exam (120 mins): is 30% of the total course grade.
Will examine all material from the whole course. The final
exam will include numerical problems as well as essays.
• Exams will cover material from BOTH lectures AND
textbook.
• The exam will consist of the same sections as before.
• Short Answer Questions
• True/False Statements
• Longer, structured answer questions.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Exam conduct
• Closed-book, no notes or textbooks allowed.
• Bring your own pens and pencils and ruler. Don’t use
correction fluid.
• No talking or other communicating between students once
the papers are distributed until they are collected.
• Cheating will be not be tolerated. If you are seen/heard to
be cheating you may be asked to leave the exam room, and
the case immediately referred to the Head of Classes in the
Astronomy Department. You will lose all credit for the exam
and your case may be referred to the University level.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Example short answer question
1. Write a brief definition of the following terms and
concepts, and give an example from the course:
a) Greenhouse effect.
b) Differentiation.
c) Doppler effect.
d) Ejecta blanket.
e) Retrograde orbit.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Example True/False Question
• Life in the Solar System. Circle the letter for each correct
answer, cross out the letter for each incorrect answer.
Then, for the incorrect answers, cross out part of the
statement which is incorrect and add replacement text to
make the sentence a true, positive statement.
• A) The two main characteristics of a living organism are
metabolism and reproduction.
• B) The last common ancestor (LCA) is the hypothesized
primate which gave rise to both chimps and humans.
• C) Amino acids have recently been found in space which
is evidence of life.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
True/False continued
• D) Water ice has been found in the polar caps of Mars.
Also, liquid water once existed on the surface of Mars,
where we believe that conditions may once have been
right for life to arise.
• E) Massive impacts were a major problem for life on Earth
in the past, possibly responsible for mass extinctions
(such as the dinosaurs). However, at the present day we
have nothing to fear from them.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Example Structured Question
•
All four of the outer gas giant planets have ring systems.
i. Describe the A, B and C rings of Saturn. Say which is the most and
least bright, and what the rings are made of.
ii. The F-ring is a strange narrow ring discovered by the Voyager
spacecraft. Why does it not spread out and disappear? Are there
similarities between this ring and the rings of Uranus and Neptune?
Explain.
iii. The rings of Uranus and Neptune are probably composed of a
different material than most of the Saturn ring particles. Say what the
differences are, and theories we have to account for this difference.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Lecture 28:
Spacecraft Exploration
of the Solar System
Picture credit: NASA/JPL
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Spacecraft
• No discussion of the planetary system would be complete without
examining the technology which supplied most of our information about
the planets: robotic spacecraft.
• Until the 20th century, planetary study was confined to telescope
astronomy: a ‘hands-off’ way of exploration which limited us to recording
what the skies wanted to show us.
• As an example, consider the far-side of the Moon. 45% of the Moon
was unseen until the first spacecraft was sent there (Luna 3, 1959).
• With the advent of large liquid-fueled rockets combined with electronic
circuits, sending probes outside the Earth’s orbit finally became possible.
• Unmanned craft came first, followed soon after by manned spaceships.
However, so far, humans have only reached the Moon, not yet venturing
beyond the Earth’s gravitational pull.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Types of Spacecraft Missions
• Spacecraft missions broadly fall into one of the following
categories:
1. Space Telescopes
2. Fly-by missions
3. Orbiter missions
4. Atmospheric probes (not designed to land).
5. Hard and soft landers
6. Rovers.
7. Hybrid/composite missions.
• We will discuss each type in turn, except #1, which are
more similar to the Earth-based telescopes discussed in
Lecture 5.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Fly-by missions
• Fly-by missions are always the first scouts sent to a
planet, on a basic reconnaissance assignment.
• They are built cheaply with a few basic instruments to
measure magnetic field properties and image the surface,
paving the way for later, more capable orbiters and landers.
• It would be impossible to design a successful orbiter, let
alone a lander, without basic knowledge of planet provided
by fly-by missions.
• We will discuss some famous robotic fly-bys, but note that
Apollo 8 was also famous as the first manned fly-by mission
of another world (the Moon).
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Voyager 1 & 2
• By far the most well-known and ground-breaking fly-by missions of all
time were the twin Voyager 1 & 2 spacecraft, discussed in detail earlier
in the course.
• In fact, Pioneers10 & 11 had already reached Jupiter (and Saturn for
Pioneer 11).
• The Voyager
missions were
famous for
achieving the grand
tour: the multiple
flybys of all four gas
giant planets that
was achieved by
Voyager 2.
Picture credit: NASA/NSSDC
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Orbiter missions
• Orbiter missions follow on from fly-by missions.
• Their purpose is usually to obtain a thorough mapping of
the planetary surface, mostly in visible light, although
sometimes radar must be used.
• The ideal orbit for this is a polar orbit, passing over both
poles, and mapping the planet as a rotates underneath each
orbital track - this is often used for the Earth.
• For planetary missions however, it is often too difficult or
expensive to reach a polar orbit, so orbiters are in equatorial
or low-inclination orbits.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Radar Mapping Mapping
• Venus poses a tougher problem for mapping than the Moon or Mars why?
• Due to the dense, cloudy atmosphere, mapping in visible light will not
se to the surface - radar must be used.
• The best ever surface map of Venus was
made by the Magellan spacecraft (artist’s
impression, right), which used an advanced
form of radar called ‘synthetic aperture radar’
(SAR) to map the entire planet down to 100
m resolution.
• The task took 2 years, from 1990-1992, and
Magellan finally returned more data than all
previous missions combined!
Picture credit: NASA/JPL
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Atmospheric Probes
• Atmospheric probes were not relevant to the exploration
of the Moon or Mars, but especially for Venus there were
many atmospheric probes (attempted landers for the most
part) before a true landing was achieved.
• In the outer solar system, Galileo carried a probe (no
name) which was dropped into Jupiter’s atmosphere,
returning the first in situ measurements of the temperature
and composition of a gas giant world.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Venus Atmospheric Probes
• Early Soviet Venera missions concentrated on
probing the atmosphere in preparation for an eventual
landing on the surface.
• The first probe to enter Venus’s atmosphere, Venera
4 (1967, right) was crushed in the atmosphere, but
showed a surface temperature of 770 K, pressure 75
bars, and an atmosphere of 90-95% CO2.
• The Venera 4 probe carried 2 thermometers, a
barometer, pressure gauge, 11 gas analyzers etc.
• Veneras 5&6 (1969, left) were also crushed, 26 and
11 km from the surface respectively. The 405 kg
entry probes were strengthened versions of Venera
4. During these descent, measurements of
atmospheric composition, temperature and pressure
were further refined.
Picture credit: NASA/NSSDC
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Landers
• The second wave of lunar missions in the early 1960s,
following the early flybys, but preceding the orbiter missions,
were simple impact-trajectory craft designed to
photograph the surface right up to the point of impact.
• In just a few years however, these missions progressed to
soft landers, paving the way for eventual human landings in
1969.
• Soft-landers are able to relay vital information about the
surface properties of a planet, especially surface texture,
slope, firmness etc - and then continue to function as
‘weather stations’ (on Mars) or seismometers (on the Moon).
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
US First Lunar Landers
• NASA’s first successful soft lander was
the 270-kg Surveyor 1 (right) on June 2nd,
1966. Six more Surveyors were launched
between 1966 and 1968.
• The Surveyors were all equipped with
television cameras, and later carried a
variety of soil measuring devices. In all,
88,000 high resolution pictures were
returned.
• A primary objective of the Surveyor
missions was to test whether the surface
was safe for manned landings. The
mosaic image (right) was taken by
Surveyor 7 in 1968 of the Tycho crater
region.
Picture credit: NASA/NSSDC
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Viking 1 & 2 Landers
• The huge landers (600 kg each) contained entire weather stations
which remained active for 6 years (Viking 1) and 4 years (Viking 2),
much longer than anticipated. Both could communicate with the orbiters,
or directly with the Earth by radio. Why?
• Landing was accomplished by 3 retrorockets with 18 nozzles each, to
minimize disturbance of the surface. Even the N2H4 fuel was purified!
• Power was supplied by 2 small
Plutonium RTG units, good for 30 W each.
Why were RTGs used, rather than solar
cells?
• One of the main objectives was to
search for life. The results of this complex
experiment are still being debated!
Picture credit: NASA/JPL
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Rovers
• Rover missions are the next logical step in surface
exploration after a lander: effectively a rover is a mobile
lander, which can carry out the science of dozens of landers
at different locations.
• When we think of rovers today we think of Mars rovers, but
these were preceded by lunar rovers.
• At around the same time that US astronauts were driving
lunar rovers, the USSR was controlling robotic rovers, which
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Later Luna Missions
• The Luna 17 mission (1970, right) was the
first USSR mission to deploy a rover on the
moon. Looking like a bathtub on wheels,
Lunokhod 1 was intended to last for 3 lunar
days, it lasted 11 (322 Earth days),
traveling 10 km, returning 20,000 pictures
and conducting 500 soil samples. The Luna
21 mission also carried a Lunokhod rover.
• Lunas 20 (1972) and 24 (1976, right)
were sample return missions. They
returned 20 and 170 grams of lunar rock
material to the Earth for study. Of course,
by then Apollo had far eclipsed these
achievements.
Picture credit: NASA/NSSDC
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Hybrid Missions
• As successes accumulated, mission planners became
increasingly adventurous with future plans.
• Later landers carried rovers, such as Luna/Lunokhod on
the Moon, and Pathfinder/Sojouner on Mars.
• Another combination was the orbiter/lander or orbiter &
atmospheric probe combination.
•In the inner solar system, this approach was used many
times at Venus (Venera), and also at Mars (Viking).
• In the outer solar system, we have Galileo and
Cassini/Huygens.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Pioneer Venus
• Pioneer Venus was a ground-breaking US
Venus mission in 1978. The mission consisted of
two spacecraft, an orbiter and a lander. The
orbiter was described in an earlier lecture, and
made an improved radar map of the surface.
Fuel ran out and it burned up in 1992.
• The lander was actually a multi-probe in 4
parts. The main bus was unprotected, and
burned up at 110 km altitude after making some
photos.
• The bus released 3 miniature spherical probes
(80 cm) which spread out to impact (no
parachutes!) on different parts of the planet. One
survived landing, but all relayed back
atmospheric data: temperature, pressure and net
radiative flux.
Picture credit: NASA/NSSDC
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Taking a Balloon Ride
• Perhaps the most eclectic mission of all time were the twin Vega 1 & 2
missions (French-USSR partnership) launched in 1984, to Comet Halley
and Venus. Each Vega Mission consisted of 3 distinct spacecraft.
• The main spacecraft were the comet-catchers, which in June 1985 flew
by Venus and gained a gravity assist to continue on to the comet.
• At Venus, a Venera-style lander
was dropped, which requires no
further elaboration.
• In addition, a 3.4 m meteorological
balloon was deployed by each Vega
which floated in the atmosphere at
50-km altitude, lasting for 2 days. On
reaching the dayside they
overheated and burst (as planned).
Picture credit: NASA/NSSDC
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Outer Solar System Exploration
• Exploring the outer solar system presents a unique set of
difficulties.
1. Timescales for missions are long, and so components must be
reliable.
2. Power is also a major consideration. Can solar power can be used?
• Very few spacecraft have been launched to the outer
planets, at least partly due to the cost and timescales of
such missions.
•
•
•
•
Pioneer 10 & 11
Voyager 1 & 2
Ulysses
Galileo and Cassini
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Instruments
• Cassini carries a large number of scientific experiments: 12 on the
orbiter, and a further 6 on the Huygens probe.
• These include both remote sensing instruments (camera, IR
spectrometers etc) and in situ experiments such as dust collectors.
• The spacecraft carries a
radar-mapper, and the highgain antenna does doubleduty as a radio occultation
experiment.
• The probe carries
instruments to image the
surface, detect and measure
gas types and concentrations,
aerosols and dust and more.
Picture credit: JPL
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Dr Conor Nixon Fall 2006
PASSIVE REMOTE
SENSING
Instruments 1: Remote Sensing
INSTRUMENT
USED ON
PURPOSE
PROS AND CONS
IMAGING
FB, ORB, PRB,
LND, ROV
Take pictures at different
wavelengths, possibly in stereo.
Always used. Cheap and light.
Must bring light source to work
in the dark!
ULTRAVIOLET
SPECTROMETER
FB, ORB
Stellar occultations of atmospheres,
composition of ionospheres and
aurorae.
Less useful when there is no
atmosphere.
INFRARED
SPECTROMETER
FB, ORB, PRB,
LND, ROV
Measures heat radiation: gives
temperatures and gas compositions.
Mainly used for atmospheric
applications - limited use for icy
surfaces, e.g. Enceladus.
ROV
Measures mineralological composition
of rocks from close range (near
touching).
Must first prepare surface, and
then be near touching to use this
in situ instrument.
ROV
Uses a gamma ray source to
distinguish rocks based on their iron
content.
This is a specific tool for rock
measurements.
ORB
Uses high-power radio waves to map
surface topography and roughness,
even through clouds.
Very bulky and power-hungry;
usually cannot use other
instruments while radar is on.
Only used for orbiters.
ORB
Laser range-finding. Used to map
surface topography and albedo.
Similar to radar, but less bulky
and power hungry. Will not work
through clouds.
FB
Radio occultations of atmospheres,
also precise tracking to determine
gravity field.
Using the spacecraft's own
communication antenna to
perform science is nearly free.
ACTIVE REMOTE SENSING
X-RAY
SPECTROMETER
GAMMA-RAY
SPECTROMETER
RADAR
LIDAR
RADIO SCIENCE
ASTR 330: The Solar System
Instruments 2: In Situ
USED ON
PURPOSE
ORB, PRB
Measures the composition of
gas directly, by finding the
Very useful where gases can
mass distribution of atoms
be directly sampled, e.g.
and ions.
Huygens probe.
PRB, LND,
ROV
Measures temperature,
pressure, moisture, wind etc
in situ.
Attached to probe or lander,
can only give info about one
site.
PENETROMETER
LND, ROV
Measure hardness or other
physical properties of soil or
crust.
Limited use, but cheap.
MAGNETOMETER
Measure magnetic field
FB, ORB, PRB strength, direction.
Can be a useful indirect probe
of the planet's interior.
DUST & AERSOL
COLLECTORS
Used to measure properties
of larger particles than the
FB, ORB, PRB mass spectrometer.
Require probe to be in contact
with the atmosphere.
INSTRUMENT
IN SITU EXPERIMENTS
NEUTRAL GAS
OR ION MASS
SPECTROMETER
WEATHER
PACKAGE
SOIL ANALYSIS
LAB
LND, ROV
Used to measure chemical
and biological properties of
soid.
PROS AND CONS
Due to the many experiments
possible, designing a chemical
lab requires some prior
knowledge of the target.
Dr Conor Nixon Fall 2006
ASTR 330: The Solar System
Quiz-Summary
1. When did we first see the far side of the Moon, and how?
2. What were the main problems encountered when trying to land and
operate a spacecraft on Venus, and how were these overcome?
3. Describe what other types of missions have been sent to Venus, other
than single landers and orbiters.
4. How has exploration of Mars changed from Mariner 2 (1965) to the
present day? What technologies are possible now that were not then.
Dr Conor Nixon Fall 2006