New concept may enhance Earth-Mars communication

Oct 16, 2009
This is an end-on view of an alternative Mars/Earth communication relay architecture option, looking into the Ecliptic plane. Credit: Credits: ESA/University Strathclyde/University Glasgow

Direct communication between Earth and Mars can be strongly disturbed and even blocked by the Sun for weeks at a time, cutting off any future human mission to the Red Planet. An ESA engineer working with engineers in the UK may have found a solution using a new type of orbit combined with continuous-thrust ion propulsion.

The European researchers studied a possible solution to a crucial problem affecting future human missions to : how to ensure reliable radio communication even when Mars and Earth line up at opposite sides of the Sun, which then blocks any signal between mission controllers on Earth and astronauts on the red surface. The natural alignment, known as a conjunction, happens approximately every 780 days, and would seriously degrade and even block transmission of voice, data and video signals.

The research findings were released this week at the 60th International Astronautical Congress (IAC), the world's biggest space event, being held in Daejeon, South Korea.

According to the paper, "Non-Keplerian Orbits Using Low Thrust, High ISP Propulsion Systems," an innovative solution to the Mars communication problem may be found by placing a pair of communication relay satellites into a very special type of orbit near Mars: a so-called 'B-orbit' (in contrast to an 'A-orbit', based on natural orbital laws).

However, to counter the effects of gravity and remain in place, they would have to be equipped with cutting-edge electric ion propulsion.

The ion thrusters, powered by solar electricity and using tiny amounts of gas as propellant, would hold the satellites in a B-orbit in full view of both Mars and Earth. The satellites could then relay radio signals throughout the Mars-Earth conjunction season, ensuring that astronauts at Mars were never out of touch with Earth.

Johannes Kepler (December 27, 1571 - November 15, 1630) was a German mathematician, astronomer and astrologer, and key figure in the 17th century scientific revolution. This image is a copy of the 1610 original in the Benedictine Monastery, Krems. Credit: Credits: Artist unknown

François Bosquillon de Frescheville, based at ESA's European Space Operations Centre, Darmstadt, is co-author of the paper together with five engineers at the Universities of Strathclyde and Glasgow, Scotland. He agreed to answer questions on the results being presented by his colleagues at IAC.

Q1. What is special about the orbital positions described in your paper?

Satellites usually follow Keplerian orbits named after Johannes Kepler, who helped discover over 400 years ago the basic mathematical equations that describe orbital motions.

Once it is launched, a satellite in unpowered free flight will essentially 'glide' through our Solar System following the troughs and crests of gravitational forces exerted on it by the Sun, the planets and other bodies, much like a surfer glides over wave tops and troughs as she surfs toward a beach. In fact, an unpowered satellite can't do anything but follow these swells of gravitational potential, which constrain its trajectory.

Q2. But if a satellite could generate continuous thrust, it could skip across these gravitational peaks and troughs?

Yes - it could jump, as you say, into another class of orbits - the B-orbits, or non-Keplerian orbits. But you have to provide some on-board means of generating a continuous thrust, pushing in a certain direction against residual gravity. Then, an entirely new set of orbital trajectories become available.

Q3. Why not simply use the thrusters that most satellites already have, like those on Mars Express or Venus Express?

Traditional thrusters use a lot of fuel, so we only fire them for short periods to kick the satellite into a new, free-flight orbit. It is prohibitively expensive in terms of weight to equip a satellite with continuous thrust capability.

But a solar electric uses electricity generated from sunlight to emit chemical ions, giving a tiny thrust - about the same force that you feel if you blow on your hand - but over time, it's enough to move almost anything. ESA's SMART-1 got to the Moon in 2004 after 16 months using ion propulsion; its thruster only generated 0.2 millimetres per second per second of acceleration, but that's sufficient!

The trick is to find possible orbital trajectories in our Solar System where such a tiny amount of thrust, applied perpendicular to the direction of the satellite's motion, can usefully keep it in a certain location, supporting scientific observations or communications, for example.

Q4. And that's when you considered the Mars radio communication problem?

Yes. It has been known for some time that, due to the natural orbital motions of the Sun, Earth and Mars, any communication relay satellite that orbits Mars in a traditional, unpowered Keplerian orbit will, at some point, be blocked by the Sun. So it will never enable continuous communications between Mars and Earth for 100% of the time. That's not good for any astronauts on Mars.

What we have shown is that if you can provide continuous thrust, a pair of spacecraft could 'hover', respectively, over a point leading, and under a point trailing, the Mars orbit, and provide continuous radio communications between Earth and Mars. You would need two relay spacecraft to cover both halves of Mars.

You would get, in effect, full-time communications to almost anywhere on the Red Planet's surface. When the Earth-Mars conjunction season is over, the spacecraft could stop thrusting, save fuel and take up regular, unpowered or near-Keplerian orbits until the following conjunction approaches, and then take up their relay positions again for the next conjunction.

We found that a pair of relay satellites would only have to switch on their thrusters for about 90 days out of every 2.13-year period, and this solution would only increase the one-way signal travel time by one minute, so it could be effective.

This is an artist's impression of Mars Express. The spacecraft left Earth for Mars on 2 June 2003. It reached its destination after a six-month journey, and has been investigating the planet since early 2004. Credit: Credits: ESA - D. Ducros

Q5. Could such a double-spacecraft, 'continuous-thrust' mission be launched today?

Well, most of the technologies are in place or are very close to being ready.

However, our research was only the first step in understanding the complex details of such a mission. A lot more work must be done to understand in detail how the satellites have to apply the thrust - for example, taking into account the natural eccentricity of the Martian orbit. Also, failure scenarios must be studied, to have a back-up plan in case one of the ion thrusters failed. In addition, as part of our research, we catalogued other possible mission profiles.

One example would be to use continuous thrust to create a fixed, virtual 'truss' between two spacecraft perpendicular to their flight direction. It would be like having the two spacecraft connected by fixed bar or rod; this could be useful for certain applications.

Another example would be to hover near one of the Earth-Sun system Lagrange points. NASA studied just such a mission profile, called GeoStorm, back in the 1990s with a view to stationing a satellite closer to the Sun than the L1 Lagrange point so as to provide improved early warning of magnetic storms caused by solar coronal mass ejections. Such a mission would have used a solar wind sail for its thrust, but it could also be done using , which can offer control advantages compared to solar sails; this must be studied further.

There's still lots to be done, but this research will help pave the way for future robotic missions to places we've never been or for a human mission to Mars.

Source: European Space Agency (news : web)

Explore further: Europe sat-nav launch glitch linked to frozen pipe

add to favorites email to friend print save as pdf

Related Stories

NASA Finishes Listening for Phoenix Mars Lander

Dec 02, 2008

(PhysOrg.com) -- After nearly a month of daily checks to determine whether Martian NASA's Phoenix Mars Lander would be able to communicate again, the agency has stopped using its Mars orbiters to hail the ...

Recommended for you

Europe sat-nav launch glitch linked to frozen pipe

13 hours ago

A frozen fuel pipe in the upper stage of a Soyuz launcher likely caused the failure last month to place two European navigation satellites in orbit, a source close to the inquiry said Wednesday.

Cyanide ice in Titan's atmosphere

15 hours ago

Gigantic polar clouds of hydrogen cyanide roughly four times the area of the UK are part of the impressive atmospheric diversity of Titan, the largest moon of Saturn, a new study led by Leiden Observatory, ...

Video: Alleged meteor caught on Russian dash cam (again)

18 hours ago

Thanks to the ubiquity of dashboard-mounted video cameras in Russia yet another bright object has been spotted lighting up the sky over Siberia, this time a "meteor-like object" seen on the evening of Saturday, Sept. 27.

User comments : 18

Adjust slider to filter visible comments by rank

Display comments: newest first

oredson
5 / 5 (3) Oct 16, 2009
Isn't this solution simpler: Park satellites at the Sun-Mars L4 and L5 Lagrange points. These points are out far enough from Mars that two of three (L4, Mars, L5) would always be visible from Earth.

Actually, I just thought of a more scalable solution yet. Park them at EARTH's Lagrange points, which would permit year-round communication to EVERY planet in the solar system (with the possible exception of Mercury).

--edit- I forgot to say that both of these solutions require exactly zero propulsion, once parked.
fuzz54
3 / 5 (1) Oct 16, 2009
Those Lagrange points are not actually points, but small orbits. My guess is that they already have satellites or small rocks parked there. But I'm just some guy and not an expert on astronomy.
david_42
1.5 / 5 (2) Oct 16, 2009
Lagrange satellites result in much longer transmission times and cannot provide full real-time coverage over a planet's surface. The L4 and L5 points do require some thrust due to perturbations from other planets.
RayCherry
4 / 5 (1) Oct 16, 2009
Placing these satellites in an orbit about Mars sufficiently distant to be 'visible' from Earth all (Earth) year round requires them to be outside the diameter of the Sun when the Sun passes between Earth and Mars. Simple, clean thinking using the Roman idea that the shortest distance ... etc, but what about solar interference of the signals passing so close to the Sun?

Although solar Lagrange points do not provide the shortest transmission distance, wouldn't they be able to maintain higher bandwidth during the solar eclipse, than direct (through the corona) transmissions that would probably have to reduce transmission speed (increase the error-correction) in order to overcome the signal disruptions?

If the solar disruptions reduces the bandwidth, it reduces the advantage of direct line of sight.

However, the Lagrange point satellites could use less thrust to remain in position and may have access to higher frequency transmissions (upto laser optical?) through 'empty space'
barakn
3 / 5 (2) Oct 16, 2009
@David,
Due to the finite speed limit of light, no satellite anywhere could provide "real-time coverage" between Earth and Mars, although you do have a point about longer transmission times. And L4 and L5 do not "require some thrust due to perturbations from other planets." You're confusing them with L1 and L2.
danman5000
2 / 5 (1) Oct 16, 2009
Also Lagrange points are just that - points - and so you would never be able to position a satellite exactly right where it needed to be to remain stationary. You would have to equip it with thrusters to make the necessary minor corrections to keep it centered on the point. Also the planetary effects mentioned above would cause problems.
taka2k7
5 / 5 (1) Oct 16, 2009
I would think a few satellites in a Mars centric highly elliptical orbit could do the same. Coronal communication could be an issue unless the Apoareion (Mars-apogee) were sufficiently large as to mitigate Coronal concerns.

Even a sufficiently large circular orbit around Mars would suffice (although you'd have to tailor the orbit to ease satellite-to-Mars comm).
oredson
5 / 5 (1) Oct 16, 2009
Also Lagrange points are just that - points - and so you would never be able to position a satellite exactly right where it needed to be to remain stationary. You would have to equip it with thrusters to make the necessary minor corrections to keep it centered on the point. Also the planetary effects mentioned above would cause problems.


Re-read the definition of L4 and L5 Lagrange points. They are the most stable of the Lagrange points. No power needed. Also, there's no reason you need the satellite to be stationary. It just needs to be in roughly the same position, so you know where to point your antennae.
oredson
5 / 5 (1) Oct 16, 2009
I would think a few satellites in a Mars centric highly elliptical orbit could do the same. Coronal communication could be an issue unless the Apoareion (Mars-apogee) were sufficiently large as to mitigate Coronal concerns.

Even a sufficiently large circular orbit around Mars would suffice (although you'd have to tailor the orbit to ease satellite-to-Mars comm).


There would still be frequent periods of no communication with Earth, because both Mars and the Sun would occlude it. Stable placement at L4 or L5 would guarantee that at least one of the satellites can see any other solar system object.
nkalanaga
not rated yet Oct 16, 2009
George O. Smith "Venus Equilateral", 1940s. Different orbit, same problem, same solution. But his was manned.
brobof
5 / 5 (1) Oct 16, 2009
Eureka! Agree with the Mars Trojan points idea. Plus you get to look at what's there. 1999 UJ7 and the aforementioned 5261 Eureka(wiki page;http://tinyurl.com/yla3nug Lots of stones with just two birds! And free comms thrown in for as long as they are there...
sender
not rated yet Oct 17, 2009
building a line of satellite buoy routers that utilize magnetospheric dynamics of the solar system..., smart
am_Unition
4 / 5 (3) Oct 18, 2009
...Actually, I just thought of a more scalable solution yet. Park them at EARTH's Lagrange points, which would permit year-round communication to EVERY planet in the solar system (with the possible exception of Mercury)...


But the L4 and L5 points are only stable in an idealized two-body system, like the Earth-Sun system. When you consider the entire solar system's influence, the L4 and L5 points will experience small perturbations, which push the satellite away without orbital corrections.

Note that all Lagrange points are positions of unstable equilibrium! Satellites currently orbiting L1 require orbital corrections from time to time, and L1, L2, and L3 are only unstable in one dimension, whereas L4 and L5 are unstable in two.

Also, how do you bring your satellite to a standstill in relation to Earth (in order to be placed at L4/L5)? Another costly burn.

Just playing devil's advocate ;)
Nik_2213
not rated yet Oct 18, 2009
Send it out along the Lo Roads ? http://en.wikiped..._Network
barakn
1 / 5 (1) Oct 18, 2009
I'm seeing a lot of misinformation about Lagrange points. L1, L2, and L3 Lagrange points are unstable as they are saddle points on a map of gravitational potential energy in a co-rotating frame of reference. L4 and L5 are hilltops on the same map, and you'd be forgive for thinking they are unstable, but they are not. The reason is because of the Coriolis force. Any perturbing force that pushes a satellite off the hill in one direction will cause the Coriolis force to act perpendicularly to that, sending the satellite into a small orbit around the L4 or L5 point. This math-heavy paper is recommended reading - http://www.physic...ange.pdf .
nkalanaga
not rated yet Oct 19, 2009
The real problem with using L4 and L5 is that they're farther from Mars than the (admittedly unstable) points here is that L4/L5 are as far from the Mars as Mars is from the Sun, which would make the total distance much greater.
oredson
not rated yet Oct 19, 2009
The real problem with using L4 and L5 is that they're farther from Mars than the (admittedly unstable) points here is that L4/L5 are as far from the Mars as Mars is from the Sun, which would make the total distance much greater.


That's not true. L4, L5 and the Sun make up an equilateral triangle, so they are *half* that distance.

Besides, you would only need to use the L4/L5 units when Mars is actually occulted. That is the original problem trying to be solved.
nkalanaga
not rated yet Oct 20, 2009
No, L4 and L5 are 60 degrees from Mars, so the equilateral triangle is Mars, L4, Sun.