Getting to Mars means stopping, landing

Apr 04, 2011 By Anuradha K. Herath
Planned entry, descent and landing sequence for the upcoming ExoMars mission. Credit: ESA

The Challenger and Columbia space shuttle disasters were perhaps two of the most prominent reminders of how crucial it is that everything work just right for a spacecraft to travel to space and successfully return back to Earth. Whether it was the failure of the seal used to stop hot gases from seeping through, or a piece of foam insulation that damaged the thermal protection system, scientists and engineers must make thousands of predictions of all the things that could go wrong during flight.

NASA’s human Mars mission presents even more challenges of sending humans safely to a farther distance and to a more dangerous environment. Designing an aircraft that can safely enter and exit Mars’ unpredictable atmosphere is a big challenge.

“Each time we fly to Mars, we learn a little more and get a little smarter,” said Walter Engelund of NASA’s Langley Research Center. “One thing we have learned is that the Mars atmosphere is certainly a big variable. It is much more dynamic than our own ’s atmosphere.”

For missions that require entry and reentry into an atmosphere, the design of the is typically guided by its EDL (entry, descent and landing) system. Engelund, along with several other NASA colleagues, published a review of the EDL systems currently being proposed for a future manned mission to Mars in a recent book titled “The Human Mission to Mars. Colonizing the Red Planet.” The book is a compilation of studies written by a team of more than 70 scientists, including four astronauts (two who walked on the Moon), offering a detailed guide of how to successfully accomplish a human mission to Mars. Engelund is the lead author of the EDL study.

Managing the Weight

So far, NASA has had six successful Mars landers: Viking I and II, Pathfinder, MER Spirit and Opportunity, and Phoenix. However, all these missions were robotic missions with vehicles that were significantly lighter than a spacecraft carrying astronauts, supplies and fuel for a round-trip. Developing systems for a manned mission to Mars will require a careful balancing act between minimizing the weight and figuring out how to use the least amount of fuel possible.

NASA has sent several successful robotic missions to Mars. Designing a spacecraft to carry humans to the Red Planet and safely back to Earth is still a challenge. Credit: NASA

On Jan. 14, 2004, President George W. Bush gave a speech at NASA headquarters outlining a "new course" for the space program that would "extend a human presence across (the) solar system."

With a reminder that it had been nearly a quarter of a century since America developed a new vehicle for space exploration, Bush issued a call for a new manned space vehicle.

"We will build new ships to carry man forward into the universe, to gain a new foothold on the Moon, and to prepare for new journeys to worlds beyond our own," Bush said.

As a response to President Bush’s vision for space exploration, NASA, in May of 2005, began the Exploration Systems Architecture Study (ESAS), which served as the blueprint for future spacecraft that would eventually send humans back to the Moon and on to Mars. NASA may or may not use the design specifications outlined in this study, but whatever architecture it eventually does use, it will be very different from the robotic mission architecture that is used today.

“When we want to send humans to the surface we are going to need an EDL system capable of delivering at least 10 times (the) mass and volume (of the current robotic missions to Mars),” Engelund said. “NASA has actually been giving some serious thought to this over the last several years.”

At least 34 million miles separates Mars and Earth (the distance between the two planets varies during their elliptical orbits around the Sun). One of the greatest design barriers engineers are facing is dealing with the amount of fuel that will be needed to send a spacecraft on such a round trip distance. More fuel means more weight, and more weight means the need for more fuel to transport that weight.

Entering the Mars Orbit with Less Fuel

For safety and operational reasons, the spacecraft that will travel to Mars will likely not land on the surface immediately upon reaching the Red Planet.

“For a human-scale mission, it is very likely that we will have a spacecraft that stays in orbit with food and supplies for the journey home, and also for a ‘safe haven’ in case something goes wrong on the surface,” Engelund said.

What scientists are envisioning is to have the entire spacecraft first enter Mars orbit and then deploy a lander down to the surface. The ability to first orbit the planet before landing on it will also give the astronauts an opportunity to observe the atmosphere to ensure that there are no dust storms or hazardous weather at the location where they plan on landing.

To enter Mars orbit, scientists are planning on using a method called aerocapture, which has never been tried before.

“One of the problems of getting a spacecraft to another planet is that we first have to get it out of Earth’s orbit,” explained Engelund. “So we have to speed it up to a high enough velocity to break [free of] the Earth’s gravity field. Then, when the spacecraft gets to its destination planet, it has to slow down enough so that it is ‘captured’ into orbit around that planet’s gravity field.”

A process called aerobraking has been used successfully in previous missions. Aerobraking uses propulsion to first insert the spacecraft into orbit (orbit capture) and then circularizes (or achieves the desired orbit, otherwise known as orbit trim) by having the spacecraft pass through the upper part of the atmosphere several times. Aerocapture, on the other hand, performs both the orbit capture and orbit trim in a single pass through the deeper atmosphere.

Typically, the slowing down of a spacecraft is done by firing retro-rockets, or rockets that fire in the opposite direction than the spacecraft is traveling. According to Engelund, this method requires a lot of fuel that has to be carried all the way until the spacecraft reaches Mars. It adds additional weight to an already heavier vehicle and is very expensive. The aerocapture maneuver instead uses the drag caused by the planet’s upper atmosphere to slow down the vehicle. The atmosphere, in this case, serves as a “brake” for the vehicle, eliminating the need for additional fuel.

Despite the advantages of using the aerocapture method, scientists also have been studying some of the drawbacks and how to deal with some of the potential problems that could arise. According to the authors of this report, historical studies have shown that aerocapture is a fairly low-risk technology. However, many of those studies were based on small payloads most appropriate for robotic missions.

During the aerocapture maneuver, the spacecraft must take a deep dive through the Mars atmosphere. The friction experienced during entry causes the energy of the vehicle’s speed to be transferred into heat. This heating will require an extra aeroshell and a thermal protection system to protect the spacecraft and everything inside. Engelund said that even with these extra components, using aerocapture will still require less weight overall than entering the Mars orbit with a fuel-driven propulsive method.

The other potential problem is with the computer software that guides the spacecraft during the aerocapture pass. The program that is used is smart enough to determine the important parameters: how deep into the atmosphere the spacecraft needs to go, how to monitor the progress in real time, and to predict when to come back out of the atmosphere to reach the correct orbit. Precision, however, is key.

“Too deep and you burn up,” explained Engelund. “Too shallow and you don’t remove enough velocity energy, and when you come back out, either you don’t get into the proper orbit or worse you don’t get into orbit at all and sail right on by the planet.”

Deeper knowledge of the Mars atmosphere will help scientists fine-tune this procedure.

“But these are all things we’ve been studying for years - in some cases decades even -- and (we) feel confident we could design an aerocapture system using current technology,” Engelund said.

Budget Permitting

In April of last year, President Barack Obama, speaking at a conference at NASA’s Kennedy Space Center, reiterated America’s commitment to sending a human to Mars.

"By 2025, we expect new spacecraft designed for long journeys to allow us to begin the first-ever crewed missions beyond the Moon into deep space,” Obama said. “We’ll start by sending astronauts to an asteroid for the first time in history. By the mid-2030s, I believe we can send humans to orbit Mars and return them safely to Earth. And a landing on Mars will follow. And I expect to be around to see it."

Since then, however, NASA has been undergoing budget cuts that will have an impact on various programs, including those that deal with designing spacecraft for long-distance flights.

“I do think NASA has decided to take a step back and look at a broad range of technology investments to enable future space exploration beyond our own Earth orbit,” said Engelund.

Some of those cuts will most likely make its way to the Mars program and determine if and when humans will be able to explore the Red Planet.

“Unfortunately, development is closely tied to budget,” said Ayanna Howard, an associate professor of electrical and computer engineering and the chair of the robotics doctoral program at the Georgia Institute of Technology. “If sufficient funding is made available, then scientists (and) engineers should be able to develop and integrate the required EDL components necessary for human Mars missions within the next 30 years. If not enough resources are allocated, this timeline might not be feasible.”

With a manned mission to Mars still requiring a great deal of research and investment, scientists and governments may have to consider alternate options if they want to see a human -- from any country -- land on Mars.

“I think there’s a real feeling that can’t afford to go it alone, and will look towards international partnerships and cooperation,” Engelund said. “Personally I think there is tremendous potential to send humans to -- and what better way to do it than with a global campaign allowing many nations to work together?”

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User comments : 14

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ACW
5 / 5 (1) Apr 04, 2011
The Mars Direct plan's use of available Martian resources for the return trip solves many of these issues.
Quantum_Conundrum
3.3 / 5 (3) Apr 04, 2011
Silly humans.

Any idea how much computers, self assembly, and robotics is going to advance in 25 to 30 years?

It is completely impractical and beyond comprehension to imagine sending three to seven guys in a tin can to mars the same way the lunar missions were done.

What I have in mind is self assembling robots and nanotechnology to mine the asterioids with un-manned automatons mining the asteriods and comets for fuel and resources to make an orbitting habitat at Mars. As well land nanomachines on mars and build ground-based habitats and return vessels (and mine the fuel to power them,) on site.

This way, the return fuel is harvested from the Solar System either on site, or from the asteroid belt (Ceres,) through an infrastructure of self replicating nano-robots.

This way, the actual manned colony vessel need not ever return, and even if it does, it need not carry the return fuel with it on it's Earth-to-Mars stage, because the return fuel will be there waiting for it.
Quantum_Conundrum
3.7 / 5 (3) Apr 04, 2011
The technologies I speak of may sound fantastic, but there is nothing in the laws of physics to forbid them.

It makes a hell of a lot more sense to launch a few pounds of nano-machines to Mars and the Asteroid belts, and let THEM build rockets and fuel canisters and habitats (and of course, more robots,) from the available materials.

This way, you only pay the launch costs of a few pounds of cargo, and the habitats and fuel for return, and indeed most of the science, are already done before the humans ever arrive.
Parsec
2.6 / 5 (5) Apr 04, 2011
QC - to you I would ask... 'Where is my flying car?' These were widely predicted as only 10-15 years away when they entered the public imagination in the 1930's and 1940's.

Answer? Its turned out that the technological challenges were small compared to the legal and insurance ones. Safety, training the public, and cost simply made them impractical. Today, you can purchase several varieties of planes you can drive, or cars you can fly, but you still have to be a pilot. And that's hard.

Nano-bots like you propose will not be available in 20 to 25 years. There is insufficient commercial interest (for the above reasons), and they are too expensive to develop without a commercial base to support them.
Beard
not rated yet Apr 05, 2011
We can look at trends that will likely continue, such as: miniaturization, Moore's law and exponentiating data storage. New technologies like strong AI or nano assemblers would cause paradigm shifts and render any 2011 prediction useless.

Self replicating and possibly AI governed von Neumann style projects are the best option for space colonies and mining operations. We'll surely pursue this technology since the rewards would be immense.

We'll know for ourselves by 2030-2040 anyway.
Quantum_Conundrum
5 / 5 (1) Apr 05, 2011
Nano-bots like you propose will not be available in 20 to 25 years. There is insufficient commercial interest (for the above reasons), and they are too expensive to develop without a commercial base to support them.


Insufficient commercial interest?

Have you lost your mind?

Do you comprehend the implications of self-assembling nanomachines for production, maintenance, cleaning, sanitation, and medicine?

We're talking about the eventual potential to make ANYTHING (or almost anything,) for about a dollar per pound.

Intel and IBM have already claimed a "clear path" to 11nm process mass production by around 2020. That's 3 times smaller in width than existing transistors, or 9 times smaller in area, and they already know EXACTLY how to do it.

Do you realize what we are already making with existing technology?

Yesterday, I found a video card on the internet that has 800 stream processors and 1GB of RAM for only $129: 16 cents per processor...
Quantum_Conundrum
5 / 5 (1) Apr 05, 2011
I mean my God.

If you have self-replicating nanomachines, you can build labor robots and solar farms for the price of DIRT, and mass produce whatever you want.

It works like this.

Right now, only positive futurists and computer geeks believe it, but in 5 to 10 years, everyone will see the progress the geeks are making, and then more people will be convinced it's possible, so they will invest and train in those fields. Then in another 5 years or so, everyone will SEE that it is definitely going to be possible and worth it, so then everyone will invest and train in those fields, and then it will happen.

We've already seen examples in the past week and the past year where relatively primitive nano-tech has incredible implications for medicine and human health.

Anyone who is not "commercially interested" is insane.
Jaeherys
not rated yet Apr 05, 2011
I would agree with QC that nanotech is the way of the future which is why I chose it for my career path. I love everything about small structures and what it may mean for our future. Although I can't put a timeframe on it as there are probably things we need to know in order to really pull this off that we haven't thought of yet (mainly how the hell do you control these things to do what you want).

Even after we have a reliable way to control, lets say, 20 nanobots, we need some pretty sophisticated software (chemware/nanoware anyone?) to control them to produce a macroscale result. Controlling a few moles of nanobots would be so difficult I wouldn't know where to begin (yet).

Although there are some interesting nano scaled devices producing certain macro scale results (cancer treatments, ect) those are still a long way off from what most people would call a nanobot.

But that's just my two cents.
Quantum_Conundrum
3 / 5 (2) Apr 05, 2011
Controlling a few moles of nanobots would be so difficult I wouldn't know where to begin (yet)...


Off-board processing, file sharing, specialization, bot heirarchies (think ant colony or Starcraft Zerg, except Nano,) and data compression.

You don't just have nanobots.

You also have "macro bots": ranging from normal computers and robots to wrist watch sized machines.

You also have "milli bots": The size between a millimeter and a centimeter. And you have "micro bots": the size between a micrometer and a millimeter.

With these heirarchies of scales, you can develop control structures able to assist the nano-scale machines in all of their tasks.

Different scale bots can serve as fast transports for smaller scale bots to deliver them to the locations they need to go.

I envision using the best of both top-down and bottom-up approaches, as humans always have.

Chewing food is a top-down process. Digesting food in the stomache and building cells are bottom-up...
Jaeherys
not rated yet Apr 05, 2011
@QC
Makes sense to me. Makes me want to right a program for demonstration :P. I guess I've been hung up on just how do you control the very small but controlling the slightly bigger would be just as important.

When the control of nano scale environments are required, it just makes sense to have a heirachy of control.

Borg nanobots would be a little bit far fetched it seems.
Quantum_Conundrum
3 / 5 (2) Apr 05, 2011
Borg nanobots would be a little bit far fetched it seems.


Think about it this way.

An Ant is a self-intelligent organism. Some studies have even identified that Ants have primitive language with distinct words.

Now consider, an Ant brain uses Neurons, and each Neuron is far, far larger than an electronic "bit" which is 3 transistors (error checking, etc,). Now the Soma of a Neuron is a disc-like shape 4 to 100 micrometers across and perhaps several micrometers thick, we'll use a round number like 10 here.

This gives a cylindrical volume of 78,000 cubic micrometers for the body of a single neuron.

A cubic micrometer is a billion cubic nanometers. So, with an 11nm process and 3d architecture, and assuming 90% wasted space in all 3 dimensions, it should be possible to fit up to 58.6 million of 11NM transistors in the volume of a single neuron, with error checking, that comes to 18.6MB of transistors per neuron volume.

How many neurons are in an Ant's brain?
Quantum_Conundrum
3 / 5 (2) Apr 05, 2011
Correction, forgot to divide bits by 8 for bytes. It's 2.325megabytes of transistors.

Now that much per neuron volume doesn't sound like a lot, but remember, that is 11nm process transistors.

Now I don't know about you, but my first "PC" was a Windows 3.1 machine converted to Windows 95, and had just 16MB of RAM.

So I wonder, how many neurons are in the brain of an Ant, or what is the volume of an Ant's brain, and this will tell how much non-volatile memory we could theoretically cram into the same space using 11nm process and assuming 90% wasted space in each of 3 dimensions for scaffolding and wires and cooling, etc.

If a Fire Ant's brain is half a cubic millimeter, for example, then you could fit 375.6 billion transistors, or after error checking, and divide by 8, etc, you have 14.577Gigabytes of transistors.

The PC I am using right now has 6 gigabytes of our primitive 2-d architecture RAM...vs what should be a relatively easy 14.5GB in the space of an ant head...
6_6
1 / 5 (1) Apr 09, 2011
I think you like talking
Shootist
not rated yet Apr 10, 2011
Getting to Mars means stopping, landing


Bah.

"NERVA would give humanity the Solar System" - Jerry Pournelle.