Space balloons at Venus, Mars and Titan

As seen from the Soviet space probe Vega 1, bright Venus was only a crescent on June 9th 1985, as it released the ball-shaped descent module located at the front of the spacecraft. For two days, the module coasted before entering the upper atmosphere of the planet. At an altitude of 61 kilometers, the ball split into two pieces. One piece continued to fall towards the surface hanging from a parachute. On the ground, it survived for only 56 minutes before Venus’ immense pressure and heat killed it.

The other piece survived for much longer. It stayed in the much cooler and less dense upper atmosphere. With it, the piece had carried an aerostat – a helium-filled balloon flying at a constant altitude. At the bottom of a 13 meter long tether the aerostat carried a small scientific probe. For two days, the probe transmitted data from the atmosphere of Venus. It managed to traverse 11,600 kilometers while operative. After it shut down, it might have travelled even further.

Space is hard. Curious as we are, we want to peer into the places most difficult to reach. Our sibling planets make this a great challenge for us. Venus has a surface plagued with intense heat and crushing atmospheric pressure. On Titan, the extreme cold temperatures will freeze a space probe to death. And Mars, as was demonstrated recently by the Schiaparelli lander, is quite a tricky planet to land on, due to the feeble atmosphere.

Therefore, engineers toil over ways to design spacecraft that can reach their destination and survive for as long as possible, thereby yielding the most amount of science possible.

The fourth way of planetary exploration

So far, scientists have used either of three mission types to perform close-up investigations of the Solar System: fly-bys, orbiters and landers. Fly-bys like Voyager 1 and 2 offer only snapshots of planets, comets, asteroids and moons. An orbiter, on the other hand, paints a global picture and can do so for a long time. It takes a lander, though, to – literally – dig into the dirt and probe the contents. The last two, orbiters and landers, yield the greatest scientific insights. In combination, they provide both the big picture and get into the gritty details. On Mars, cooperation between rovers and satellites have been crucial to the confirmation that Mars was once a warm and wet planet.

However, the Vega 1 mission and its sister Vega 2, offer a fourth mission type – a sort of middle ground between a lander and an orbiter. Floating in the atmosphere, the Venusian aerostats survived for much longer than the landers that accompanied them and gathered scientific data that would be difficult or impossible to get from space. To date, only the Vega missions used this concept for planetary exploration.

Balloons have several advantages. They can survive for long periods in the atmospheres of hostile planets such as Venus. In addition, they are relatively cheap. Since wind will drag the balloon around, it requires no propulsion system to move. In contrast, landers stay where they land. This limits the area of exploration. Of course rovers can potentially cover great distances but their need of electric engines, wheels and gears make them complicated machines that have to be steered carefully in order for them to operate for a long time. An orbiter requires thrusters and fuel to make inclination changes that can take it to where it wants to go. The delicate fuel must be managed by foolproof systems that add to the cost.

By design, balloons need none of this. This saves mass and time spent on controlling the probe and therefore also money. On Earth, balloons are so cheap that universities around the globe use them as student-projects, to explore the stratosphere or test hardware for CubeSats.

Also, the atmosphere is quite an ideal place to study a planet from. While satellites can see almost everything from orbit, they can’t fly in the atmosphere. Air acts like a brake and orbiters are dependent on maintaining orbital speed. Otherwise, they crash into the planet. This means that satellites above worlds with atmospheres are limited to how close they can get to the surface. This enhances the need for bigger telescopes to obtain good resolution of the surface. A balloon, since it flies much closer to the planet, could use smaller telescopes and still achieve higher resolution than an orbiter.

Of course, resolution is highest on the ground. The surface is dangerous, however. A rover has to avoid sharp rocks, boulders, chasms, sand dunes and pits. The teams behind Curiosity and Opportunity work laboriously to find the safest routes for the rovers. In addition, planetary protection regulations force the rovers to take paths that keep clear of areas where life on Mars might be dormant.

A balloon simply floats above all the dangers and limitations. From a safe distance, it can study landscapes that might be unreachable for a rover. Some design studies even suggest that balloons could travel down to the surface and collect samples much like a rover would.

Wherever the wind blows

This all sounds very good, but there are downsides to the balloon design.

The most obvious one has to do with steering. As mentioned, the wind will provide the balloon with movement. This is okay, if you as a scientist are indifferent towards where your probe is going. In real life, though, most scientists don’t have the luxury of being indifferent. They want to go to specific places. This is difficult with a balloon. Unlike airplanes, balloons don’t have an aerodynamic design that helps them steer through the atmosphere. They just drift with the wind.

One solution to the problem is to make a blimp, which means shaping the balloon as an ellipsoid for greater aerodynamic properties and outfit it with propellers. However, this adds more mass, that could have otherwise been delegated to scientific instruments and also a blimp is much more complicated than an aerostat.

I met a Ph.D. student from NC State University, who had a mass-efficient and simple solution to the problem. His name is Christopher Yoder and he wrote me this in an email:

“One major downside of balloon missions is that their trajectory is governed by the wind, which is great because it passively propels the system around the planet. However, the balloon has to go where the wind currents take it, thus making station keeping or travelling to specific locations difficult. One method of solving this problem is to hang a sail from the balloon and guide the balloon using aerodynamic lift force generated by the sail (lift force being perpendicular to the relative wind direction, not to be confused with the buoyant force keeping the sail aloft). This method requires little power to operate and has the potential to provide trajectory control over long periods of time.”

The Mars pumpkin balloon, Venus surface-sample return and a Titan blimp that heals itself

Christopher Yoder is not the only person, who has worked on designs for planetary balloons. At the southern tip of the Big island of Hawaii, where the rocky coast line meets the deep-blue Pacific Ocean, a group of engineers from NASA’s Jet Propulsion Laboratory (JPL) gathered in the summer of 2002. The weather there is consistently good but the engineers hadn’t come to enjoy the sun or the water. Instead, they chose the place because weather conditions allowed for a test of their two balloon prototypes.

The prototypes had been designed with Mars exploration in mind. After inflation, the first would take the shape of a sphere, as most balloons do. It was made of light but flimsy Mylar film. The other had the shape of a pumpkin and was made of heavy, but strong, polyethylene film. Each prototype was carried by balloon to an altitude of 34 kilometers. Then they were released, a parachute opened and the prototypes began inflation. The spherical balloon did not survive the test, but the pumpkin design did.

The test on the Big island of Hawaii was a culmination of five years of research. In 1997 JPL had initiated the Mars Balloon Validation Program. They drew inspiration from the Vega missions and wanted to make a balloon that could explore Mars.

Mars has almost no air. Therefore, a balloon has to be very big in order to float and preferably be made of very light material. But first it has to be deployed after entering the atmosphere. A balloon that is snapped out of a container by a parachute at supersonic speeds experiences a lot of stress. This increases the risk of breaking the light plastic it is made of.

In order to make the balloon more resilient to the stresses of aerial deployment, the engineers had designed the second balloon with tendons. These, besides making the balloon more robust, also gave it the shape of a pumpkin.

However, this might still not be enough. Jeffery Hall who worked on the test wrote this to me in an e-mail:

“Balloons are viewed as less likely to be used for Mars exploration because of the difficulty of solving aerial deployment and the inflation problem. In the forseeable future, existing orbiting and roving vehicles already have the ability to meet the challenges of Mars exploration.”

Jeffery has, however, also been involved with other concepts. In 2006 he and a team of engineers from JPL, NASA Wallops and ILC Dover, built a 5.5 meter spherical superpressure balloon that could fly at an altitude of 55 kilometers in Venus’ atmosphere. They even tested how a teflon coating could protect the balloon from the acidic air of Venus.

Such a vessel could possibly descend to the ground, scoop up some dirt, ascend and launch the surface sample on a small rocket back to Earth. There is even the possibility that balloons such as this one could search for life in the Venusian air. Microbes might thrive in the upper parts of the atmosphere, where conditions are hospitable to life.

In another paper of his, Jeffery also explored how to make a blimp that could survive for a long time in the cold atmosphere of Titan.

See, the one thing that limits the lifespan of a balloon are pinholes. On Earth, the amount of pinholes in a balloon wil build up over time, because the change of temperature that follows from night and day makes the plastic stretch and retract. The same thing would happen in the atmosphere of Titan, the only difference being, that there would be no humans around to patch up the balloon and refill it with helium or hydrogen, once the balloon had too many pinholes in it.

If you get wounded and lose blood, your body will replenish the blood, if the wound is sealed. Imagine if you could duplicate this in a balloon. This was exactly what Jeffery and his team did. They came up with a gas management system that could convert methane into hydrogen. Titan’s atmosphere is comprised mainly of nitrogen, but a little over 1 percent is methane. Using a small chemical reactor, the hydrogen molecules in the methane could be stripped from the carbon molecule and thereby keep the blimp buoyant. Still, since nobody would be around to seal the pinholes, the blimp would still leak, but the constant intake of new hydrogen would cancel out the loss of buoyancy. The blimp would also be outfitted with a nitrogen removal system that would make sure that the gas within the blimp is not polluted by the – in comparison to hydrogen – heavy nitrogen.

Some of the balloon designs at the facilities of JPL. (Source: JPL)

Such a system could extend the lifespan of a Titan blimp to a year or longer. NASA has, in its deliberations about how to further explore Titan, looked to balloons as a possible exploration design.

Bad times for planetary balloon research

I get excited when I read about concepts such as these. It therefore also makes me sad to report that JPL has not continued their work on planetary balloon research. The work on Mars balloons ended in 2008. In 2013 the work on Venus balloons also stopped and some work on Titan balloons continued until 2014. Jeffery Hall and some of his colleagues are trying to re-start the development of Venus and Titan balloons. I hope they will succeed in this endeavor.

Ballons seem so archaic. Yet, they continue to stir the fantasy of so many people within many different fields of work. Although the Hindenburg burned up in a fiery blaze, today airships are on the way back, as means of transporting people and goods. Project Loon seeks to deliver internet around the world with continously floating balloons, and NASA has been doing astronomy with stratospheric balloons for years now.

Though work on planetary balloons might now not be moving forward right now, the potential is still there. It might be our only way to really explore Venus and for Titan the design could get us closer still to that strange moon. In the future, I hope to see pictures taken from the end of a tether that is connected to a balloon floating high over an alien landscape.


Further reading

V. V. Kerzhanovich, J. A. Cutts, H. W. Cooper, J. L. Hall, B. A. McDonald, M. T. Pauken, C. V. White, A. H. Yavrouian, A. Castano, H. M. Cathey, D. A. Fairbrother, I. S. Smith, C. M. Shreves, T. Lachenmeier, E. Rainwater and M. Smith, Breakthrough in Mars Balloon Technology,” Advances in Space Research, Vol. 33, 2004, 1836-1841.

J. L. Hall, V. V. Kerzhanovich, A. H. Yavrouian, G. A. Plett, M. Said, D. Fairbrother, C. Sandy, T. Frederickson, G. Sharpe, and S. Day, Second generation prototype design and testing for a high altitude Venus balloon,” Advances in Space Research, Vol. 44, 2009, pp. 93-105..

J. L. Hall, J. A. Jones, L. Brooke, B. Hennings, R. Van Boeyen, A. H. Yavrouian, J. Mennella and V. V. Kerzhanovich, Gas management system for an ultra long duration Titan blimp,”Advances in Space Research, Vol. 44, 2009, pp. 116-123.






Elon Musk and everyone else are preparing for Mars

I didn’t travel 17 hours from Denmark to Guadalajara (Mexico) to drink tequila and lie on the beach. Instead, I had traversed the 9,600 kilometers (5,900 miles) to spend five days in a congress-center with an air-conditioning system that was a bit too cold for my regular outfit of jeans and a t-shirt. This should have come as no surprise to me; the International Astronautical Congress is an annual event that attracts mainly gray-haired men from aerospace companies and universities around the world who wear black business suits and ties. During the 5-day long event these men are busy swapping business cards, giving presentations and holding meetings – all of which demands an indoor climate substantially cooler than the Mexican outdoors.

I hadn’t brought any business cards; my purpose was to witness the Elon Musks keynote on making humans a multiplanetary species.

The first thing I noticed when walking in through the big glass entrance was the emphasis on Mars. Lockheed Martin – main sponsor of IAC 2016 – featured a video outlining the “Mars Base Camp” concept at their exhibition. According to this, astronauts will go into orbit around The Red Planet in a space station assembled in Lunar orbit, thus paving the way for human footprints on the red, rusty surface sometime in the 2030’s. Also, the company had put these stickers on the congress floor:


Sunday before the congress actually got started, I attended my first series of lectures. Buzz Aldrin, the second person to walk on the Moon, gave a lecture on how to send multiple spaceships to The Red Planet, by having them in constant orbit between the Earth and the Moon and the Moon and Mars. Before him, a person from the Chinese Space Agency outlined the future for their space program, which includes an orbiter and a lander mission to Mars in the beginning of the 2020’s.

On the day of the official opening the Director General of ESA, Jan Wörner, said; “Everybody wants to go to Mars”. He, however, advocates for going back to the Moon first and establish a base on the lunar South Pole. A concrete roadmap for this plan remains to be seen, and Wörner calls the “Moon Village” a concept, rather than a strategy already being developed. Currently ESA is building the service module for NASA’s Orion capsule – an essential piece of hardware for NASA’s “Journey to Mars”.

So the talk about going to our red neighbor planet started just as the congress opened its doors to the 4,000 delegates attending. But the talk was still to come.

Early morning – the 27th of September – delegates gathered in front of the shut doors guarding the main plenary hall. By each passing hour the crowd grew larger. Elon Musks speech wasn’t even due before 14.30. When the doors opened people ran to get a good seat and even the VIPs crammed the entrance. Excited as everybody else around me to see Elons plan I sat down in the fourth row. The lights dimmed and a circular screen turned into the planet Mars. Elon Musk got on stage, illuminated by bright spotlights. He gave his talk.


I won’t bother you with the details of his speech. The sort of people reading a blog entry like this probably already know the specific impulse of the Raptor engine and the crew capacity of the Interplanetary Transport System. Anyway, if you don’t know the details, watch Elons speech here.

Every conversation after the presentation echoed Musks vision. Each person I talked to had a slightly different reaction to it; Some complained about the silly Q&A, some lamented the lack of details and yet others were dumbstruck with amazement and couldn’t wait to buy a ticket to Mars.

I was so fortunate as to sit next to Robert Zubrin the following day, who is the founder of the Mars Society and author of the book The Case for Mars. We were chatting and he invited me to sit in on an interview he was doing with Joe Mascaro, a blogger for Now Space.


Joe wrote an excellent article on the conversation that you should definitely read (click here!). Also, listen to this podcast where Zubrin is interviewed about the Interplanetary Transport System.

In summary, Robert Zubrin has some serious concerns regarding the Interplanetary Transport System. According to him, the spacecraft is overkill; sending humans to Mars does not require a vessel with 150 tons of dry mass and a speedy travel time of down to 80 days.

“People who are going to spend the rest of their lives on Mars don’t care if the trip takes three or six months,” Zubrin said. By using a slower travel time than the one proposed by Musk and by relying on smaller spacecraft, a more effective system could be devised.

Although Zubrin views the Interplanetary Transport System as a “suboptimal design” he holds Elon Musk in high regard.

“Do you think he [Elon, red] is an explorer?” asked Joe Mascaro. Zubrin paused for around a minute.

“Elon is a hero,” he then said. According to Zubrin, the South African entrepreneur has definitely rocked the aerospace industry and now everybody wants to go to Mars.

Other concerns besides the design were raised at the congress. Bill Nye from the Planetary Society had also attended the presentation and he praises the vision but doubts people will choose to live under the harsh conditions of Mars. Also, he warns that colonists could wipe out evidence of past or present life on The Red Planet, by spreading microbes from Earth that would be difficult to distinguish from possible Martian life.


Check out Loren Grush’ piece on the Interplanetary Transport System, where she also interviews Bill Nye (click here!).

After a presentation on the scientific results of New Horizons, I talked to a NASA official who liked Elons idea, though, he and many others regard funding as the biggest challenge for SpaceX to overcome. Elon Musk suggested jokingly in his presentation “Stealing underpants” and “Kickstarter” as possible sources of funding.

The money-problem might be the real reason for him to present his plan at IAC. The Interplanetary Transport System is essentially an empty space-train, where private and state actors in partnership can decide what goes to Mars. Elons speech was therefore primarily addressed to the many representatives from aerospace companies and space agencies sitting in the dim congress-hall, rather than to SpaceX fans from Denmark or Mexicans girls wanting to give Elon a kiss. In a press conference after the presentation, Musk stated that as of now, only five percent of the SpaceX workforce is working on the Interplanetary Transport System. In the future more effort will be put into the project.

Jeff Foust from SpaceNews wrote a good piece on this, which you can read by clicking here.

It took me some days to digest what the Interplanetary Transport System actually is. The thought of the giant spaceship and the even bigger booster was like a splinter in my mind. Something about it seemed unreal (besides the fact that it has not yet been constructed). Then it hit me; this isn’t a spacecraft. At least, it’s not useful to think of the Interplanetary Transport System as a vehicle in the same category as the Saturn V or the Vostok 1. Those rockets were like the Wright Flyer (the airplane that the Wright brothers constructed) – essentially experimental vehicles that proved successful and carried astronauts into space but with no direct commercial value. The Interplanetary Transport System on the other hand is a modern day passenger plane. Like a Boeing 747 it gives consumers the possibility of buying a seat on a ride from A to B – only this ride takes you to another planet. It needs to have commercial value from the start. Otherwise it won’t work.

From an aesthetical point of view, the Saturn V has always been the prototypical spacecraft in my mind. Towards the top it got pointier and pointier and it ended, like the graphite at the end of a sharpened pencil, with the launch escape tower at the tip of the rocket. Pictures of fiery stage separations come to mind when thinking of the Saturn V; each separation dooming a giant fuel tank to its graveyard on the bottom of the ocean.

The Interplanetary Transport System is an entirely different creature in comparison. When I first saw it, I thought; “SpaceX has really managed to outdo themselves in their efforts to make rockets look even more phallic”. Make a model of the rocket that could fit in your hand and I bet most people would mistake it for a sex toy.


This vehicle has no launch escape tower, nor does it have stages in the conventional sense of the term. Instead it consists of a booster and a spacecraft. The spacecraft alone takes up 40 percent of the entire length of the vessel. Compare that to the length of the Saturn V third stage, which only took up about one sixth (16.6%) the length of the entire rocket. Elon Musk seems to have trashed conventional wisdom within rocket science that says; “Big rockets carry small paylods” and replacing it with his own insight; “Giant rockets carry big spacecraft”.

Much like modern airplanes don’t need to be biplane or be made of wood, the Interplanetary Transport System is not expendable and does not come with a launch abort system. At the press conference after his speech, I asked Elon about the abort capabilities of the vessel. He said that “the spaceship can fly away from the booster if there’s a problem at the booster level” but added;

“Launch abort on the spaceship itself is kind of pointless. If you’re on Mars you’re taking off or you’re not taking off. The key is to make the spaceship itself extremely safe and reliable, and have redundancy in the engines, high safety margins and have it be well tested. Much like a commercial airline; they don’t give you parachutes.”

I filmed only the bit after I had asked the question and you can watch the clip here. Also, you can find the full transcript of the press conference by clicking here.

It will be exciting to follow the development of the Interplanetary Transport System. Humans travelling to Mars will be the adventure of our lifetime. However, one question that I still have, has to do with the versatility of the spacecraft. Musk only hit upon this very briefly at the end of the presentation, where he imagined the vessel landing on Saturns moon Enceladus or going into orbit around Jupiter. But I think there are lower hanging fruits than the outer planets. How about using the Interplanetary Transport System as a cruise ship in LEO or even in Cis-Lunar space? I can imagine a lot more people wanting to go on a short trip into space, rather than spending the rest of their lives on Mars. Personally, that seems much more appealing to me. Using the spacecraft as a cruise ship could thus be part of creating the necessary funding for the Mars-colony and serve as a testing ground at the same time.

Also, I view this as a great opportunity for scientific missions. Normally, scientific space missions consist of a probe and a team of scientists. With the Interplanetary Transport System you could ditch the probe and send the scientists directly to the object of investigation. Like Darwin travelled the Earth in search of scientific discoveries, scientists of the future may visit the worlds of the Solar System and uncover great secrets.

I had, and still have, a feeling that IAC 2016 and Elon Musks speech will end up in the history books. Certainly, if he actually succeeds with his endeavour, the future scholars on Mars will point to Guadalajara as the place where it all started. I’m very happy to have been part of that.