The story of CubeSats – satellites as small as a water
bottle—reminds me of the first years of personal computers. In their earliest years, personal computers –
or microcomputers as they were often called – were built and used by hobbyists
who enjoyed geeky tinkering and firmly believed that this infant technology had
the potential to revolutionize the world.
(I wanted to get my own microcomputer, but as a fresh college grad, I
had to wait a few years until dropping costs and my income found a happy
meeting point.)
To date, CubeSats largely have served as education platforms
used to train university students in the basics of building a simple
spacecraft. A number of space agencies
and laboratories, though, are now working to evolve these tiny spacecraft so
they can take on serious scientific studies, including missions to the moon,
asteroids and planets.
CubeSats were invented in 1999 at Stanford University to
enable university students to design, build, and fly real satellites. In the fifteen years since, the standard has
taken off with satellites built by numerous universities and several space
agencies all contributing to the 138 launches listed by Wikipedia (which admits
that its list is incomplete).
A basic CubeSat is 10 x 10 x 10 cm (1 liter) satellite that
weighs no more than 1.3 kilograms.
Within that space, the satellite has to perform all the essential
functions of a satellite: power, command and control, communications, and
possibly operate a payload that makes some type of measurement. The specification allows for cubes to be
stacked to create spacecraft of 2, 3, 6, and 12 liters, or units (U) as they
are called, to be built. (A 3 U CubeSat
is about the size of a loaf of bread.) The
total cost for developing a simple CubeSat can be as low as $10,000 (although
launch costs can be as much at ten times that).
Today, technology has advanced to the point that several
projects are underway to build CubeSat-inspired spacecraft for lunar and
planetary exploration. One of the
reasons I say ‘inspired’ is that while many of the proposals would be based on
CubeSat 3 U and 6 U sizes, some of the designs use different forms factors
while still maintaining the spirit of a nano-spacecraft (less than 10 kilogram) design.
The other reason I say ‘inspired’ is that a planetary
CubeSat will have to take on challenges that their predecessors haven’t. For many CubeSat missions to date, the focus
has been on the learning experience for students, and high reliability and
long-life have not been goals. Also, all
CubeSats have orbited the Earth where the magnetosphere shields them from
radiation, sunlight is plentiful, and communicating with stations on the Earth
is simple.
To operate in deep space to explore the solar system,
engineers are taking on the challenges of building reliable, long-lived
spacecraft, adding radiation hardening, fitting propulsion systems within the
tiny form factor, and communicating across tens and hundreds of millions of
miles. Then there’s the challenge of
miniaturizing instruments so they can return data worth the costs of the
mission within the tight space, weight, power, and communications restraints of
CubeSats.
In addition, many of the challenges of operating and
navigating a planetary mission remain the same whether the spacecraft costs $1M
or $1B. Designers of planetary CubeSats
will need to develop new ways to run these missions at a fraction of what
traditional missions have cost. (One big
challenge: While electronics grow ever cheaper, salaries for mission operations
engineers don’t.)
In other words, CubeSats for lunar and planetary missions
are a work in progress.
I’ve talked with several people knowledgeable about
planetary exploration about CubeSats, and their reactions range from enthusiasm
to outright skepticism that that these ‘toys’ can be scaled up to meet the
challenges of planetary missions.
I spent 25 years in the high tech industry, often working
with teams of engineers developing cutting edge technologies. I learned that if the base technologies exist
(you couldn’t have asked an engineer in the 1970s to build a CubeSat), then
smart engineers will find a way to do it.
I also learned that the cost of achieving these breakthroughs is often
higher than you expect. Planetary
CubeSats are likely to cost in the millions of dollars apiece, and the total
cost to make planetary CubeSat technology off-the-shelf equipment may be
several tens of millions of dollars. Even
at $5M a pop, though, a CubeSat mission would still cost just a few percent of
the cost of the smallest planetary missions in flight today. For comparison, many instruments on planetary
spacecraft cost millions and tens of millions of dollars.
Another thing I learned in the computer industry is that
size and cost revolutions don’t make the big machines obsolete. The market for big, expensive mainframe
computers is alive and well despite personal computers and smart phones (and in
many ways, because of them); the new technologies just made mainframes awesomely
more capable than their predecessors.
We will still need highly capable, large, and expensive
planetary missions to answer our questions about the solar system. CubeSats and nano-spacecraft, I believe, will
fill holes where the larger missions don’t go or will serve as auxiliary
spacecraft for their bigger brethren. I
expect they also will serve to train new generations of engineers and scientists
who can learn their arts on inexpensive missions.
I expect that in ten to fifteen years planetary CubeSats
will be a proven approach. It will help
that scientists studying the Earth and cosmos also see promise in CubeSats. Their efforts to build reliable, capable nano-spacecraft
also will advance the technological base.
So what might the next decade of planetary CubeSat missions
look like? The examples that follow
provide a sampling of the ideas being developed or proposed. I emphasize that this is a sample of the
ideas. In the week or so it’s taken me
to write this, I’ve come across at least a half dozen new concepts and I’ve
left out a number of concepts I already knew about.
If you’d like to see more examples of mission concepts and
technologies, look at the presentations from these recent lunar,
Mars, and asteroid
workshops.
INSPIRE
 |
| More information here and here. Credit: JPL/NASA |
The first CubeSat mission into deep space will likely be
JPL’s twin INSPIRE spacecraft. The goal
is to prove the technologies and operations to enable future missions. The only destination is to get tens of
millions of kilometer into deep space while operating a simple payload (a
magnetometer and camera). The design problems the engineers are having
to overcome are the same that all future planetary CubeSat missions will face,
making this mission a pioneer. I’m not
aware that a launch date has been set.
Lightsail
 |
| More information here. Credit: The Planetary Society |
The Planetary Society is planning to launch its own
CubeSats, two Lightsails, to test solar sail technology in Earth orbit. Propulsion is a key challenge for
CubeSats. They are too small to carry
significant rocket fuel, and they are often launched as secondary payloads with
large satellites whose owners don’t want to incur the risk of launching with an
inexpensive CubeSat carrying explosive rocket fuel. Solar sails use the minute pressure of
sunlight to propel themselves. The
Planetary Society has raised funds from private citizens to build their two
spacecraft, with the first launch is scheduled for May 2015. (Other teams are also developing propulsions
systems that use other technologies such as low-thrust systems that melt solids
to produces low thrust electrosplays.)
Near Earth Asteroid Scout
 |
| More information here for the Scout mission; here for the solar sail. Credit: NASA. |
The Near Earth Asteroid Scout CubeSat mission will marry
technology developed for the INSPIRE mission with a small solar sail system
developed by NASA’s Marshall Space Flight Center. The mission team will need to develop methods
for precision deep space navigation and operation to allow its CubeSat to perform
a slowand close flyby of its target
asteroid. As the spacecraft closes in on
a small asteroid, it will take images in four colors with
resolutions of as high as 10 cm per pixel.
The spacecraft will be carried aloft on the first flight of NASA’s Space
Launch System (SLS), currently expected in 2018.
Lunar Flashlight
 |
| More information here. Credit: JPL/NASA |
The Lunar Flashlight mission is the third approved planetary
CubeSat mission that I am aware off.
Like the Near Earth Asteroid Scout, it will use a solar sail, in this
case to propel itself to the moon and enter orbit. Once in orbit, the spacecraft will make use
of the highly reflective sail to cleverly solve one of the problems of lunar
exploration. Thanks to previous
missions, we strongly suspect that the permanently shadowed, extremely cold
craters at the moon’s southern pole harbor some amount of ice. What we don’t have is a map of the
distribution of those ices because, well, it’s dark in those craters and
cameras and imaging spectrometers see only shadow. The Flashlight spacecraft will use its solar
sail to reflect sunlight into the craters, providing the light needed for the
mission’s spectrometer to map the distribution of ice over the course of 78
orbits. Like the Scout mission, the
Flashlight mission will require a reliable spacecraft (the mission will take
approximately 21 months to complete), precision navigation, and sophisticated
operations on a nano-spacecraft budget.
Also like the Scout mission, the Flashlight mission will launch on the
first SLS flight.
ExoPlanetSat
With the Earth-orbiting ExoplanetSat telescope, we move from
approved, funded missions to concepts for possible CubeSat missions. A joint project of the Massachusetts
Institute of Technology and Draper Laboratory, this spacecraft would, like the
Kepler mission, discover planets by watching them transit in front of their
stars. Where the Kepler mission watched
thousands of distant stars at a time, the ExoplanetSat mission would watch a
single, bright, nearby star, with the first, prototype spacecraft focusing on
the Alpha Centauri system. If the first
spacecraft successfully proves the technology, the mission’s proposers hope to
launch a number of these spacecraft to watch other nearby stars. This approach would get around the problem
that bright nearby stars are scattered across the sky and cannot be
simultaneously watched by a single spacecraft.
(For more information, see here.)
Lunar and Mars Water Distribution
Missions (LWaDM and MWaDM)
 |
| More information for the lunar concept here, for the Martian concept here, and for the BIRCHES infrared spectrometer here. Credit: NASA |
A key question for both our moon and for Mars is how the
distribution of water and ice varies across their globes with the time of day
and location. These CubeSat missions
would use miniaturized infrared spectrometers to map water across their
surfaces. The spectrometer for these
missions would be a miniaturization of the 11 kilogram New Frontiers Pluto
spacecraft’s instrument to ~2 kilograms.
These presentations are frank about the challenges facing
designers of planetary CubeSats.
The proposers state that supplying sufficient power and
relaying data back to Earth are two key challenges. For the former, they propose to use next
generation solar cells; for the latter, they propose to relay data through
larger spacecraft in orbit around these worlds.
At Mars, the large, traditional orbiters such as the Mars Reconnaissance
Orbiter and MAVEN carry relay systems designed to support lander and rover
missions. These larger orbiters could also relay data from orbiting
CubeSats.
The presentations also list a number of other design
challenges including how these spacecraft would be placed in orbit, thermal and
radiation protection, and sufficient autonomy to operate with low cost mission
support. Exposing design issues such as
these is one of the important roles of these early concepts; they focus
attention on areas where solutions are needed.
Several teams are working on enhancing the communications
systems of CubeSats. Once concept from a
team at JPL, for example, would support data rates from Mars of 8,000 bits per
second compared to 500,000 to 4,000,000 bits per second for the Mars
Reconnaissance Orbiter. If a Martian
CubeSat satellite has to relay its own data back to Earth, though, operating
the communications system and the scientific instrument at the same time may
stress its power system.
Mars Weather Satellite Network
 |
| More information here. Credit: NASA. |
The small size and low cost of CubeSats allow scientists to
propose networks of spacecraft that make simple measurements at several places
at once. Traditional large spacecraft
typically carry highly capable instruments, but the cost of the spacecraft and its
instrument often limits the mission to a single orbiter that can take
measurements at just one location at a time.
Many of the proposals for CubeSats for Earth observation are for
networks of satellites that make simple simultaneous measurements at multiples
places across our globe.
The instrument proposed for these Martian weather satellites
would have two spectral channels, a single detector per channel, and a single
telescope. The equivalent instrument on
the Mars Reconnaissance Orbiter now at Mars has nine spectral channels, 21
detectors per channel, and two telescopes optimized for observations in
different spectral bands.
Dandelion Mars Lander
 |
| More information here. Credit: Malin Space Science System and Stellar Exploration. |
Concepts for planetary nano-spacecraft aren’t limited to
orbiter and flyby spacecraft. The
Dandelion concept would place several CubeSat-sized landers on Mars to make simple
dispersed seismic and weather measurements.
The lander looks rather like an upside down umbrella with a 3 U (10 x 10
x 30 cm) CubeSat as the handle. During
descent, the lander would descend with the decelerator – what looks like the
canopy of an umbrella – pointed down to slow the lander to enable a soft
landing. After touchdown, the craft
would deploy solar cells, a seismometer, and a mast with cameras and
meteorological instruments. Then each
lander would then patiently gather data over the next Martian year (two Earth
years), relaying its data through an orbiter back to Earth.
One advantage of the Dandelion concept, and another proposal
called MarsDrop, is that multiple small landers could be carried by a larger
mission, such as the 2020 Mars rover. The
MarsDrop presentation, though, mentions that development of the first lander
might come with a hefty (for a nano-spacecraft mission) price tag: $20-30M. (See this presentation
for more about the MarsDrop proposal.)
Other concepts, such as the Hedgehog,
propose to deploy nano-landers on asteroids to explore the surface under the
guidance of a nearby mother craft.
Europa
 |
| Credit: NASA. |
NASA plans to launch a large Flagship mission to Europa in
the 2020s that will cost around $2B.
Last year, NASA’s Jet Propulsion Laboratory solicited ideas from
universities for CubeSat spacecraft that could serve as auxiliaries to enhance
the mission. JPL selected ten concepts
from universities for further study.
Little information was released on the proposals other than a curt
statement that read, “The universities' Europa science objectives for their
CubeSats would include reconnaissance for future landing sites, gravity fields,
magnetic fields, atmospheric and plume science, and radiation measurements.” I’ve heard rumors that one or more of the
proposals may include long-lived CubeSats that would make multiple encounters
with Europa. I suspect that these
proposals may be for CubeSats that would conduct magnetometer or radio science
flybys that would study the ocean depth and perform gravity studies of the
moon’s interior. Both studies would
require simple payloads and low data rates but many passes close to Europa and
each CubeSat pass would add to the number the mother spacecraft does. Perhaps one or more proposals would orbit
Jupiter from outside the high radiation fields to continuously scan Europa from
afar for active plumes of water and ice expelled from the ocean beneath the icy
crust. Other proposals might include
CubeSats that image the surface from heights too low to be deemed safe for the
main, expensive spacecraft.
Jupiter Atmospheric Probes
 |
| More information here. Credit: J. Moore/York University |
Sometimes, being tiny may be an enabling capability in its
own right. NASA once had the technology
to build and test heat shields that could withstand the searing heat of entry
into Jupiter’s atmosphere by a large probe, which enabled the Galileo mission to
do so in 1995. Since then, that entry technology
has been lost and it is too expensive to replicate.
A team lead by John Moores from the Centre for Research in
the Earth and Space Sciences (CRESS) at the York University in Canada has
proposed that a spacecraft could carry up to six atmospheric probes that
incorporate CubeSat technologies to make them small and lightweight. The peak heat load these probes would
experience during entry would be one-seventh that of a traditional large probe,
enabling these probes to be built with existing entry technologies. Each probe would be too small to carry a full
complement of instruments, so the instruments would be divided among the
probes.
Jupiter’s atmosphere is complex and the Galileo probe
studied it in just one location that turned out to be atypical. Micro-probes might allow scientists to study
additional locations from within Jupiter’s atmosphere.
Small Innovative Missions for Planetary
Exploration (SIMPLEX)
In December of 2014, NASA released an announcement of
opportunity for teams to propose a new planetary CubeSat mission. The request specifies, “This solicitation
supports the formulation and development of science investigations that require
a spaceflight mission that can be accomplished using small spacecraft…
Investigations of extra-solar planets are not solicited... Proposals to this
program element may propose to use 1U, 2U, 3U, and 6U form factors… This
program element encourages, but does not require, the submission of CubeSat
investigations that operate in interplanetary space, and would, therefore, meet
more demanding engineering and environmental requirements than has been
experienced by previous CubeSats. While it is expected that proposed
investigations would involve some advanced engineering development of
instruments and/or spacecraft systems technology, all proposals must include a
science investigation that will return and publicly archive usable scientific
data and result in the publication of results in refereed scientific journals… Proposals
should plan on launch readiness by September 30, 2018… The Life Cycle Cost of
an investigation selected through this solicitation may not exceed $5.6M.”
Multiple space agencies have shown that they are serious
about developing the technologies for scientific CubeSat missions. This latest request from NASA gives the
scientific community a chance to propose their ideas to both develop the
potential of CubeSats and to conduct meaningful a scientific mission. I’m looking forward to seeing what creative
idea is selected.
