Bridging the Gap Between Space Station and Mars: The IMUSE Strategy (1985)

NASA's sprawling Dual Keel space station design in 1986. Niehoff's Interplanetary Platform would have resembled the crew-tended freeflyer located at top left. Image credit: NASA.
In common with many space advocates past and present, I long for the day when humans set foot on Mars. In addition to being a fascinating place to explore, it is the world most like Earth in our planetary system (though it is still very alien).

We have a lot of work to do to get ready to go to Mars. Before we can plan long-term stays (the most economical kind), we need to determine whether martian gravity, which pulls with only one-third the strength of Earth gravity, is adequate to halt (or at least dramatically curtail) bone loss and other afflictions of microgravity. We also need to determine as best we can whether life exists there.

The level of effort we invest in seeking to ensure that we do not damage a martian biota through careless introduction of Earth microorganisms will say much about us as a species. Two salient facts should be kept in mind as we consider the question of how best to interact with life on Mars: first, Earth and Mars are probably very similar a few kilometers down, where we find abundant chemosynthetic life on Earth (that is, Mars is likely to be, like Earth, warm and wet below the surface); second, life formed early and rapidly on Earth, but it remained unicellular until just about 600 million years ago. Mars life, if it exists, might now be in a process of retreat, a rear-guard action leading, perhaps, to extinction as the planet cools and dries out; alternately, it might be biding its time.

That we know neither whether the human body can withstand Mars conditions for prolonged periods nor whether Mars life (if it exists) can withstand unharmed the microbiota the human body carries with it indicates that, for now, we should take a cautious approach to humans on Mars. That does not mean we should sit forever in low-Earth orbit. On the contrary, it means that we should seek to accomplish intermediate goals which themselves are important and exciting.

Intermediate steps would link where we are (a space station in low-Earth orbit and remote-controlled rovers, landers, and orbiters slowly exploring Mars) with where we logically should be headed (a science base at Mars with a long-term human population — think Antarctica — working closely with teleoperated machines). Achievement of that goal could in turn lead where some of us believe we would like to be (a permanent, self-sustaining Mars colony serving as a jumping-off place for a new branch of humanity).

I like how John Niehoff's Integrated Mars Unmanned Surface Exploration (IMUSE) strategy logically ties together the NASA automated and piloted space programs. This has been attempted many times over the years — below I will mention one such attempt, the joint Jet Propulsion Laboratory (JPL)/NASA Johnson Space Center (JSC) Mars Sample Return (MSR) studies of the 1980s — but it has always run into institutional barriers or tripped over new, typically ill-considered, large-scale moon/Mars initiatives.

Niehoff was the manager of the Space Sciences Department at Science Applications International Corporation (SAIC) when, on 30 July 1985, he presented his IMUSE strategy to the National Academy of Science Space Science Board Major Directions Summer Study. He proposed employing reusable automated spacecraft with designs "deeply rooted" in planned U.S. space station technology to carry out a complex, evolving series of automated Mars Sample Return (MSR) missions between 1996 and 2016.

His work had its origins in the 1984 joint Jet Propulsion Laboratory/NASA Johnson Space Center MSR study and the work of the National Commission on Space (NCOS), a blue ribbon panel appointed by President Ronald Reagan at the insistence of Congress to chart a future for the U.S. in space. Former NASA boss Thomas Paine chaired the NCOS, which included such luminaries as Neil Armstrong, Sally Ride, and Chuck Yeager. Niehoff and SAIC provided both the JPL/JSC MSR study and the NCOS with planning and engineering support.

Niehoff explained that linking MSR with the Space Station Program would integrate it with "other capabilities and objectives of the larger space program." It would also create a bridge between early 1990s Earth-orbital station operations and a piloted Mars landing in the early 2020s.

At the time Niehoff made his presentation, the Space Station Program was just 18 months old. Reagan had used his January 1984 State of the Union Address to launch (in a bureaucratic sense, at least) the manned space laboratory. He gave NASA until 1994 to complete it.

NASA and its contractors studied a range of possible station configurations in 1984-1985. They had in fact begun concerted station planning before the first Space Shuttle launch in 1981. In early 1986, six months after Niehoff's presentation to the Major Directions Summer Study, NASA settled on the ambitious Dual Keel station design. The Dual Keel would provide ample facilities for space construction and satellite servicing and a home base for space tugs that could launch or retrieve spacecraft and satellites.

Niehoff's IMUSE spacecraft — which he dubbed an Interplanetary Platform (IP) — would transport smaller vehicles between Earth and Mars. It would provide them with "keep-alive" solar cell-generated electrical power, thermal control, course-correction propulsion, and other requirements typically provided by an expendable spacecraft bus.

The IP would cut costs over the course of the IMUSE program because it would need to be launched onto its interplanetary path only once. As the IP flew without stopping past Mars or Earth, the smaller vehicles it supported would separate to land on or go into orbit around the planet or would leave the planet to rendezvous and dock with the it.

Had Niehoff's IMUSE proposal gone ahead (and used his first scenario), the Interplanetary Platform would have been en route to its first Mars encounter at the time the Hubble Space Telescope captured these images. Image credit: NASA.
Niehoff described a pair of IMUSE scenarios. In both, the IP would follow SAIC-developed Versatile International Station for Interplanetary Transport (VISIT) cycler orbits, which, he explained, would be "simultaneously resonant with both Earth and Mars." A spacecraft in a VISIT-1 orbit would circle the Sun in 1.25 Earth years, which meant that it would encounter Earth four times in five Earth years and Mars three times in two Mars years. A VISIT-2 orbit, on the other hand, would need 1.5 Earth years to complete. A spacecraft on a VISIT-2 path would encounter Earth twice in three Earth years and Mars five times in four Mars years.

Niehoff's first IMUSE scenario would begin with Earth-orbit departure of one 6340-kilogram IP — possibly pushed by a Space Station-based space tug — in May 1996. During its first Mars encounter (December 1997), the IP would drop off a 400-kilogram "smart rover" capable of complex autonomous operations and a 1110-kilogram communications orbiter for relaying radio signals between Mars and Earth. The rover and orbiter, packed separately in identical 2570-kilogram streamlined aerocapture vehicles, would skim the martian atmosphere to slow down so that Mars's gravity could capture them into orbit.

The rover would then descend to Mars's surface atop a 1170-kilogram "generic lander" capable of precision landing. After rolling off the lander onto the surface, it would employ a variety of scoops, picks, and drills to gather rock, sand, and dust samples.

In April 2001, a second rover and two 4300-kilogram Mars ascent vehicles would rendezvous and dock with the IP as its Sun-centered orbit carried it past Earth for the first time. This would demonstrate "hyperbolic rendezvous" ahead of its use in the piloted Mars program. Hyperbolic rendezvous would occur not in Mars or Earth orbit, but rather in the IP's orbit around the Sun. The technique would save propellants because the IP would not fire rocket motors to capture into and escape from Earth or Mars orbit.

Seven months later (November 2001), the IP would swing by Mars for the second time and drop off the 2001 rover, which would land at a new site on Mars. Ascent vehicle #1, meanwhile, would land near the 1996 rover and ascent vehicle #2 would set down near the 2001 rover.

Earth would not be positioned properly for the IP to make a direct return after the November 2001 Mars encounter, so the IP would orbit the Sun twice and return to Mars for the third time in July 2005. Ascent vehicle #1 would lift off from Mars bearing the 10 kilograms of samples the 1996 rover collected and ascent vehicle #2 would lift off bearing 2001 rover samples. The ascent vehicles would perform hyperbolic rendezvous and dock with the IP as Mars slowly shrank behind the three spacecraft.

In April 2006, the IP would swing by Earth for the second time to drop off the Mars samples it had collected 10 months earlier. A Space Station-based tug would rendezvous and retrieve the samples after they aero-captured into Earth orbit. The IP would also pick up ascent vehicle #3 and two 2000-kilogram automated Mars surface stations.

It would release these during its fourth Mars encounter in April 2009. Ascent vehicle #3 would land close to the still-operational 1996 rover. The surface stations would land at separate sites, bringing to four the number of Mars landing sites explored in the IMUSE program. The stations would conduct life science experiments, test manufacture of propellants from martian resources, and study the effects on spacecraft materials of long exposure to martian surface conditions.

During its third Earth encounter (April 2011), the IP would pick up a "manned precursor payload" consisting of equipment and supplies for the first piloted Mars landing expedition. It would drop off the manned precursor payload in December 2013, during its fifth Mars encounter, and pick up samples from the 1996 rover launched from Mars by ascent vehicle #3. In April 2016, the IP would encounter Earth for the fourth and final time to drop off the samples.

Niehoff's second IMUSE scenario would employ two IPs. These would deliver the same payloads to Mars in the same manner as his first scenario, but would start later and then proceed at an accelerated rate. The first IP would leave Earth in July 1998 and fly past Mars in February 2000, November 2003, August 2007, and May 2011. It would encounter Earth in July 2003, July 2008, and July 2013. IP #2 would leave Earth in April 2001, fly past Mars in November 2001, July 2005, and April 2009, and encounter Earth in April 2006 and April 2011. IMUSE scenario #2 would return the first Mars samples to Earth in April 2006 and drop off the first piloted program precursor payload at Mars in May 2011.

The piloted program, which eventually might employ large cycling spacecraft based on Space Station modules and other hardware to rotate crews to and from a long-term Mars surface outpost, would commence shortly thereafter. Piloted cyclers might travel permanently in VISIT-type orbits, becoming in effect space stations in solar orbit. The NCOS timetable called for a Mars surface outpost to be in place by 2035, 50 years after Niehoff presented his study.


"Integrated Mars Unmanned Surface Exploration (IMUSE), A New Strategy for the Intensive Science Exploration of Mars," J. Niehoff, Science Applications International Corporation; presentation to the Planetary Task Group, Major Directions Summer Study, Space Science Board, National Academy of Science, 30 July 1985.

Pioneering the Space Frontier: The Report of the National Commission on Space, Bantam Books, May 1986.

More Information

Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

A Bridge from Skylab to Station/Shuttle: Interim Space Station Program (1971)

Making Rocket Propellants from Martian Air (1978)

The Collins Task Force Says Aim for Mars (1987)


  1. Did the IMUSE documentation give any consideration to how to "space-harden" the IP so that it would survive for the (quite lengthy) number of years it was planned to be in use?

  2. I don't find anything like that in Niehoff's presentation - if there's a more extensive document out there somewhere, perhaps it addresses this issue. My thought is, however, that the IP would be built like the Space Station, which would be expected to remain functional for an extended period. Of course, the IP would not have astronauts on hand to perform servicing EVAs. Perhaps we could look to some of the early long-lived robotic missions - Viking and Voyager had both functioned longer than expected at the time of Niehoff's presentation.


  3. True; ISEE-3 has certainly shown us how long some space-based technology can still function in a hostile environment.

    I was wondering about the docking ports. Particularly in the long, multi-orbit period between dropping off the Ascent Vehicles and collecting them again; plenty of time for lubricants to leak/evaporate, or material encountered en-route to gum up the works.

  4. A space engineer told me once that, once a spacecraft is in space, it's in a benign environment. When things go wrong, it's typically something inside the spacecraft at that point, not something from outside. Sure, there's thermal cycling, radiation, all that, but one can design for those things, especially if your spacecraft is operating in an environment that has been well characterized (say, GEO).

    Niehoff isn't clear about the design of the docking systems, though my sense is that they would be relatively simple. There'd be neither a pressurized tunnel nor a hatch, for example. They'd actually be more like berthing ports. There would, however, be services passing from one spacecraft to another (probably often going in both directions) - electricity, coolant, data, etc. But experience with the Space Station (which was meant to include automated tugs and freeflyers that would come and go frequently) would probably enable NASA and its contractors to build and prove reliable reusable automated connectors for fluids and electricity ahead of IP development.



  5. This IMUSE concept looks smart but I have serious doubts about its usability for science missions, because the scenario seems cast in stone once the spacecraft is launched. Scientific instruments and technological developments face many unexpected obstacles (e.g. the recently delayed InSight mission). IMUSE sounds like a recorded music where live performance is necessary.

    I am quite eager to read uour future post about possible future steps!

  6. Simon:

    I don't think IMUSE is different from current Mars exploration in that regard. The IP would provide basic services, and those wouldn't vary from one mission to the next; likewise, the generic lander. The science payloads could change over time, though the main focus of all science would be sample return, which narrows down the range of useful instruments. I think there'd be more latitude with regard to the orbiter science payloads.

    IMUSE is in fact a bridge linking Space Station with piloted Cycler spacecraft, which would be like space stations orbiting the Sun. Though I know many people find the idea peculiar, I've always thought it nifty. You could build up a big spacecraft with lots of shielding and room for passengers, and the only vehicles would would need to speed up/slow down at a planet would be small one-way cargo carriers and round-trip piloted taxis. One could aerocapture at Earth and Mars and make propellants on Mars for the taxi return trip.


    1. Is this similar to the idea that Buzz Aldrin has promoted to link Mars & Earth with continuously orbiting Cycler spacecraft?

  7. It's the same idea, though Buzz has worked with folks at Purdue and other places to design some new trajectories. Hollister and Minovitch did the first rigorous work on cycling trajectories in the 1960s (Minovitch, as you might know, is the mind behind the gravity-assist concept).



I like hearing from my readers. No rules except the obvious ones - please keep it civil and on topic.

Advertiser comments have led me to enable comment moderation.