Artist's concept of NASA's Voyager spacecraft. Image credit: NASA/JPL-Caltech
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Every mechanic loves to tinker with a machine to give it optimum operating efficiency. But this latest engineering feat involving the Voyager 2 spacecraft wins the prize for longest distance tune-up. Akin to servicing an old car to increase gas mileage, engineers at JPL sent commands across 14 billion kilometers (9 billion miles) out to Voyager 2, enabling it to switch to the backup set of thrusters that controls the roll of the spacecraft. This will reduce the amount of power that the 34-year-old probe needs to operate, giving it better “gas mileage” and — hopefully — the power to operate for at least another decade.
The move was a little risky, as these backup roll thrusters were previously unused. It meant trusting equipment which has been idle and out in the harsh environment of space for 32 years to work — and keep working for the remainder of the mission.
“The switchover is pretty permanent – the thrusters are not rated to be reused after being unheated,” said the @NASAVoyager2 Twitter feed.
Voyager 2 will save about 11.8 watts of electric power by turning off the heater that kept the hydrazine fuel to the primary thrusters warm.
Voyager 1 and 2 are each equipped with six sets, or pairs, of thrusters to control the pitch, yaw and roll motions of the spacecraft. With this latest command, both spacecraft are now using all three sets of their backup thrusters.
The primary roll thrusters now turned off fired more than 318,000 times. Voyager 1 changed to the backup for this same component after 353,000 pulses in 2004.
Projected levels of the Voyagers' RTG levels. Credit: @NASAVoyager2 Twitter Feed.
The rate of energy generated by Voyager 2’s Plutonium 238 nuclear power source continues to decline, and is now down to about 270 watts from the 470 watts being produced when the spacecraft launched in 1977. But now, by reducing its power requirements, engineers expect the spacecraft can continue to operate a bit longer.
Still, at the rate of decay, the Voyager spacecraft won’t have sufficient electric power to its instruments sometime by the mid-2020’s.
Using solar power for a spacecraft traveling beyond Jupiter is impractical, (which is why it is important that Congress pass a bill to restore funding for production of Plutonium 238).
Heliocentric distances for Pioneer, Voyager and New Horizons. Credit: NASAVoyager2 Twitter feed.
The Voyagers are on their way toward interstellar space, beyond our solar system, where no human spacecraft has been before. This latest tune-up will hopefully get Voyager 2 a little farther while she’s still able to communicate with Earth.
Phobos-Grunt Model. This is a full-scale mockup of Russia's Phobos-Grunt. The spacecraft was supposed to collect samples of soil on Mar's moon Phobos and return them to Earth for study. Credit: CNES
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Editor’s note: Dr. David Warmflash, principal science lead for the US team from the LIFE experiment on board the Phobos-Grunt spacecraft, provides an update for Universe Today on the likelihood of saving the mission.
The Phobos-Grunt probe is still stuck in orbit around Earth. However, periodically the spacecraft experiences a mysterious slight boost in its orbit. Following the first episode where this occurred, commentators speculated as to the cause. The activation of the spacecraft’s thrusters – the small engines that are designed to steer the craft and make small adjustments — was an obvious answer.
Is spacecraft trying to save itself?
The spacecraft is not responding to any communications, and engineers at the Russian Space Agency Roscosmos have decided that the craft had reverted to a safe mode after the engine of the Fregat rocket stage that was to propel her from a low to a higher orbit around Earth failed to ignite. While in safe mode, the craft had oriented herself to the Sun, using the thrusters to adjust her roll, pitch, and yaw. But to change the parameters of the orbit, she’d need to accelerate, so there was speculation that the needed thrust had come from leaks and venting of gases in a direction favorable to increased orbital stability.
After a second episode during which the altitude increased again, according to Ria Novosti editor-columnist of the journal “News of Cosmonautics” Igor Lisov has reported that a source in the space industry had explained that the probe “Corrects her orbit” every now and then.
Corrects her orbit? Does this mean that the probe knows where she is?
Probably not.
With information coming from Roscosmos being so scarce, reporting on the mission that began was launched on November 9, 2011 has depended on a few official statements from the agency, augmented by speculation from various space experts. Being in safe mode, Grunt simply is waiting for instructions –instructions that controllers are having difficulty delivering, because initial communication was not supposed to take place with the probe at such a low orbit.
If Grunt’s safe mode includes a program that fires thrusters every so often to keep the craft from entering the atmosphere in the event of a malfunction just after reaching low Earth orbit, no statements from Roscosmos have mentioned it, thus far. Whatever the reason, if it continues to occur, we can expect that the predicted date of atmospheric entry will be moved back again, just as it was moved from late December/early November to mid-January after the first orbital correction episode.
The Planetary Society’s Living Interplanetary Flight Experiment (LIFE) capsule, on board the Phobos-Grunt spacecraft. Credit:The Planetary Society
What might this mean for the mission? First of all, perhaps it could buy more time for controllers to establish communication –although Roscosmos has stated that December is the limit for correcting the problem, despite the fact that the probe will be in space at least until mid January. The second thing it could do would be to keep the Planetary Society’s LIFE experiment in space a little longer, which would have benefits only if the Grunt return capsule containing the LIFE biomodule separates from the rest of the craft and makes the reentry and landing that it was designed to do at the end of the flight. This possibility and the potential scientific value is discussed in my previous update, Might the LIFE Experiment be Recovered?
As for the question of why a craft that merely is supposed to find the Sun while in safe mode fires thrusters in a direction that improves the orbit, perhaps it is just good luck, or perhaps it really is part of the safe mode. Until Roscosmos provides more information of what may have caused this, the reason for the orbital correction remains a mystery.
An artists concept of the Phobos-Grunt Mission. Credit: Roscosmos
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Editor’s note: With Russian engineers trying to save the Phobos-Grunt mission, Dr. David Warmflash, principal science lead for the US team from the LIFE experiment on board the spacecraft, provides an update of the likelihood of saving the mission, while offering the intriguing prospect that their experiment could possibly be recovered, even if the mission fails.
With the latest word from Roscosmos being that the Mars moon probe, Phobos-Grunt is “not officially lost,” but yet remains trapped in low Earth orbit, people are wondering what may happen over the next several weeks. Carried into space early Wednesday morning, November 9, Moscow time, atop a Zenit 2 rocket, Grunt, Russian for “soil”, entered what is known in space exploration as a parking orbit. After the engine of the Zenit upper stage completed its burn, it separated from another stage, known as Fregat, which now still remains attached to Phobos-Grunt. Ignition of the Fregat engine was to occur twice during the first five hours in space. The first Fregat burn would have taken the spacecraft to a much higher orbit; the second burn, about 2.5 hours later would have propelled the probe on its way to Mars and its larger moon, Phobos. From this moon, a sample of soil would be scooped into a special capsule which would return to Earth for recovery in 2014.
Grunt is still in a low orbit, because neither Fregat burn occurred. While the spacecraft is believed to be in safe mode and even has maneuvered such that its orbital altitude has increased, controllers have been unable to establish contact to send new commands. If communication cannot be established, it will re-enter the atmosphere.
In addition to the sample return capsule, Grunt carries an instrument package designated to remain on the Phobosian surface, plus a Chinese probe, Yinghuo-1, designed to orbit Mars. The mission also includes the Planetary Society’s Living Interplanetary Flight Experiment (LIFE) , for which I serve as principal science lead of the US team. Carried inside the return capsule into which the Phobosian soil is to be deposited, LIFE consists of a discoid-shaped canister, a biomodule, weighing only 88 grams. Inside are 30 sample tubes carrying ten biological species, each in triplicate. Surrounded by the 30 tubes is a sample of soil with a mixed population of microorganisms, taken from the Negev desert in Israel to be analyzed by Russian microbiologists.
The Planetary Society’s Living Interplanetary Flight Experiment (LIFE) capsule, on board the Phobos-Grunt spacecraft. Credit:The Planetary Society
Organisms carried within the LIFE biomodule include members of all three domains of Earth life: bacteria, archaea, and eukaryota. The purpose of the experiment is to test how well the different species can endure the space environment, akin to microorganisms moving in space within a meteoroid ejected from Mars by an impact event. If organisms can remain viable within rock material that is transferred naturally from Mars to Earth, it would lend support to the Mars transpermia hypothesis –the idea that life on Earth may have began by way of a seeding event by early organisms from Mars.
We know of microorganisms that could survive the pressures and temperatures associated with the ejection itself. We also know that during atmospheric entry, only the most outer few millimeters of rocks are heated on their way to Earth; thus, anything alive in a rock’s interior at this point should still be alive when the rock hits Earth as a meteorite. If life forms also could survive the journey itself from Mars to Earth, a Martian origin for Earth’s life would be a major possibility. It also would mean that life originating on its own anywhere in the Cosmos could spread from each point of origin, thus increasing the number of living planets and moons that may exist.
Numerous studies of the survivability of many of the LIFE species have been conducted in low Earth orbit, but much of the challenge to life in space comes from highly energetic space radiation. A large portion of space radiation is trapped by a system of magnetic fields known as the Van Allen radiation belts, or the geomagnetosphere. Since very few controlled studies of microorganisms, plant seeds, and other life have been conducted beyond the Van Allen belts, which reach an altitude of about 60,000 kilometers (about 1/7th the distance to the Moon), the Planetary Society arranged to have the LIFE biomodule carried within Grunt’s return capsule.
Over last weekend, the spacecraft surprised everyone by maneuvering on its own, raising its orbit. Due to this, the estimated reentry date was moved back from late November to mid January, meaning that the LIFE biomodule will be in space for more than nine weeks. An intriguing possibility that looms as controllers consider how the mission might end is that the Grunt sample return capsule will break off from the rest of the craft intact. If this happens, it could assume the stable atmospheric entry, descent, and landing that were expected after the return from Phobos. If this happens and the capsule comes down on land, we could recover the LIFE biomodule and test the state of the organisms packaged within it. The result of yet another biological test in low orbit, it would not be the experiment of our dreams. But, amidst the loss of a mission into which so many engineers and scientists have invested their dreams, a little bit could mean a lot.
An illustration showing the ESA's Mars Express mission. Credit: ESA/Medialab)
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Mars Express has been a fixture in orbit around the Red Planet for almost eight years, but problems with the spacecraft’s computer memory has put the orbiter into safe mode and science observations have been halted for the time being. The spacecraft has gone into safe mode three times since mid-August, twice being recovered successfully. It has also had additional problems with its memory during this time. ESA says a technical work-around is being investigated that will enable the resumption of a number of observations, which will hopefully evolve into a long-term solution.
Safe mode is operational mode designed to safeguard both the spacecraft itself and its instrument payload in the event of faults or errors.
The portion of Mars Express’s computer the Solid-State Mass Memory (SSMM) system, which stores data before sending it on to Earth was not able to either write new data or read the previous data already in memory. The SSMM is a critical subsystem, central to all spacecraft and instrument operations.
Timeline of recent safe mode and anamolous events for Mars Express. Credit: ESA
This is not the first time the spacecraft has gone into safe mode. Three years ago a similar event took place, but now this multiple occurrence of problems has the Mars Express team looking for inventive solutions. The memory system has been switched to the “B” side or redundant computer, but the same fault took place, putting the spacecraft back in safe mode.
Another issue with the spacecraft going into safe mode is that is uses a lot of reserve fuel – as much as is required for six months of normal operations — so the frequent instances of this mode has engineers looking for a long-term solution. Most of the fuel consumption when entering safe mode is the ‘Sun acquisition’ process for letting the spacecraft know where it is in space, which requires a significant amount of spacecraft maneuvering.
ESA says they are making good progress with finding an alternative approach to commanding Mars Express, and will test it soon, and work continues on the finding a full solution to the memory problems.
GRAIL and its Delta 2 rocket on the launchpad. Credit: Alan Walters (awaltersphoto.com) for Universe Today.
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High upper level winds put a damper on hopes for launching the GRAIL mission on its first attempts on Thursday, September 8. While the weather looked perfect on the ground at Kennedy Space Center, weather balloons showed high winds in the region of the atmosphere where the Delta 2 launcher would normally experience the most turbulence.
NASA will try again on Friday, September 9 with two one-second launch windows available at 8:33 and 9:12 EDT (12:33 or 13:12 UT). There were two one-second launch windows for Thursday, and both were “red” because of the winds aloft.
The dynamic duo twin-spacecraft Gravity Recovery and Interior Laboratory (GRAIL) mission is designed to map the Moon’s gravity with extreme precision.
Low periapsis Narrow Angle Camera image of the Apollo 17 Landing Site. Image is 150 meters wide, Credit: NASA/GSFC/Arizona State University.
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New images of the Apollo 12, 14 and 17 landing sites are the highest resolution pictures ever of human forays onto another world, as seen from a bird’s eye view — or in this case, a satellite’s eye view. The Lunar Reconnaissance Orbiter dipped to a lower altitude, just 21 kilometers (13 miles) over the lunar surface.
“We like to look at the Apollo landing site images because it’s fun,” said LRO principal investigator Mark Robinson at a media briefing today. “But LROC (Lunar Reconnaissance Orbiter Camera) is looking at the whole Moon, and we have now taken 1,500 of these very high resolution images from all around the Moon which will help scientists and engineers to plan where we want to go in the future.”
Apollo 17 landing site taken by LRO in its lower orbit, with 25 cm per pixel. Credit: NASA/Goddard/ASU
Apollo 17 landing site from the regular 50 km altitude and about 50 cm per pixel. Credit: NASA/ Goddard/ ASU Compare in the images above the Apollo 17 landing site with 25 cm per pixel (top) and 50 cm per pixel (bottom).
Most notable are the tracks where the astronauts walked show up better, and details of the landers/descent stages can be resolved better.
Robinson said he was looking at the new images of the Apollo 17 landing site in Taurus Littrow Valley with Apollo 17 astronaut Jack Schmitt and Schmitt said “You need to image the whole valley at this resolution!”
This is the third resolution of Apollo sites that the LRO team has released — the first came from LRO’s commissioning phase where the altitude was about 100 km and the resolution was about 1 meter per pixel; next came the release of images from an altitude of about 50 km, with a resolution of about 50 cm per pixel; and now from about 21-22 km altitude with a resolution of 25 cm per pixel.
“These are the sharpest images of Apollo landing sites we’ll probably ever get with LRO,” said Rich Vondrak, LRO project scientist, “as we’ll never go as low in altitude as we were in the past month.”
LRO has now returned to its circular orbit of 50 km above the surface. This altitude requires monthly reboosts and since keeping LRO in that orbit would quickly exhaust the remaining fuel, in mid-December, LRO will move to an elliptical orbit, (30 km over south pole and 200 km over north pole). LRO will be able to stay in this orbit for several more years.
“This has been a highly productive mission, releasing a total of 245 terabytes of data — which would be a stack of 52,000 DVDs,” Vondrak said. Next week the science team will put out their 7th public release of data to the Planetary Data System, making all that data available to the public.
The paths left by astronauts Alan Shepard and Edgar Mitchell on both Apollo 14 moon walks are visible in this image. (At the end of the second moon walk, Shepard famously hit two golf balls.) The descent stage of the lunar module Antares is also visible. Credit: NASA's Goddard Space Flight Center/ASU
Robinson noted that the details of what pieces of equipment are in each location are verified by images taken from the surface by the astronauts. He was asked about the flags and if they are still standing: “All we can really see is the spots where the flag was planted because the astronauts tramped down the regolith. I’m not sure if the flags still exist, given the extreme heat and cold cycle and the harsh UV environment. The flags were made of nylon, and personally I would be surprised if anything was left of them since it has been over 40 years since they were left on the Moon and the flags we have here on Earth fade after they are left outside for one summer. If the flags are still there they are probably in pretty rough shape.”
The tracks made in 1969 by astronauts Pete Conrad and Alan Bean, the third and fourth humans to walk on the moon, can be seen in this LRO image of the Apollo 12 site. The location of the descent stage for Apollo 12's lunar module, Intrepid, also can be seen. Credit: NASA/Goddard/ASU
Since we can still see the tracks and equipment looking unchanged (at least from this vantage point) one reporter asked if these items will be on the Moon forever. “Forever is a long time, so no, they won’t be there forever,” Robinson replied. “The Moon is constantly bombarded by micrometeorites, and slowly over time the tracks will disappear, then the smaller pieces of equipment will disappear, and eventually the decent stages will probably get blasted by an a larger asteroid. The estimate is that rocks erode 1 mm per million years. In human terms it may seems like forever, but geologic terms, there will be no traces of Apollo exploration in 10 to 100 million years.”
This video shows more info and a “zoom in” of the sites:
Jane Houston Jones from JPL provides information on what’s up for September, focusing on the Moon. The next few days will be a good time to look for the Apollo landing sites — and no, you won’t be able to see any details from Earth, even with a good telescope, but it is fun to try and locate the areas humans have walked on the Moon. Jane shows you how. And of course, the GRAIL mission to the Moon is scheduled to launch on Sept. 8. Learn more about the mission here.
And as a heads up, look for new images of the Apollo landing sites from the Lunar Reconnaissance Orbiter that will be released next week. LRO recently moved closer to the Moon to take new and improved images of these historic sites. We’ll share them as soon as they are available.
A 'rock garden' around the rim of Endeavour Crater, as seen by the Opportunity rover. Credit: NASA/JPL/Caltech; 3-D by Stu Atkinson
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Want to experience a “you-are-there” moment with the Opportunity rover on Mars? Grab a set of 3-D glasses (red/blue) and take a gander at one of the latest views from Oppy as she starts her explorations around the rim of Endeavour Crater. This stunning 3-D version of an image taken by the rover was created by our pal Stu Atkinson. This “rock garden,” as the folk from Unmanned Spaceflight are calling it, provides a view unlike anything either Mars rover has investigated yet on Mars. The region is called “Spirit Point” in honor of the now-silent rover that sits on the other side of Mars. This is actually an ejecta field of rocks thrown about after the impact that created this huge crater where the rover is now traversing, and is an exciting region for the MER scientists to explore. As Stu so poetically says in his Road to Endeavour blog, it’s also exciting because Opportunity “was sent to Mars to look at rocks, to drive between rocks, to trundle over powdery, cinnamon-hued dust that used to be rocks to get to younger, more solid rocks.”
Oppy’s found a veritable treasure trove of interesting rocks to explore, and Stu has also put together a collection of some of the most interesting in the rover’s current field of view:
The Rocks of Spirit Point. Images: NASA/JPL/Caltech; collection by Stu Atkinson
The latest mission update for Opportunity on the Mars Rover website says the rover has now reached the rock named Tinsdale 2, started a multi-sol, multi-target in-situ (contact) investigation with a Microscopic Imager (MI) mosaic of a set of surface targets collectively named “Timmins,” followed by a placement of the Alpha Particle X-ray Spectrometer (APXS) for an overnight integration. So, she is putting all her resources to work to find out more about this interesting rock.
Here’s a non-3-D, raw image of the region from Opportunity:
Opportunity's view of Endeavour Crater on sol 2696, from the navigation camera. Credit: NASA/JPL/Caltech.
Thanks to Stu for sharing his great images, and you can read more about this interesting spot on Mars in Stu’s article, “In Praise of Rock“
Just what will the GRAIL mission to the Moon do? Find out in just over 3 minutes with this new video about the mission. The launch of GRAIL is scheduled for Sept. 8, 2011 from Cape Canaveral Air Force Station in Florida.
A human mission to an asteroid. Credit: Lockheed Martin
Imagine, if you can, the first time human eyes see Earth as a distant, pale blue dot. We’ve dreamed of deep space missions for centuries, and during the Apollo era, space enthusiasts assumed we’d surely be out there by now. Nevertheless, given the current state of faltering economies and potential budget cuts for NASA and other space agencies, sending humans beyond low Earth orbit might seem as impossible and unreachable as ever, if not more.
But NASA has been given a presidential directive to land astronauts on an asteroid by 2025, a mission that some say represents the most ambitious and audacious plan yet for the space agency.
“The human mission to an asteroid is an extremely important national goal,” Apollo astronaut Rusty Schweickart told Universe Today. “It will focus both NASA’s and the nation’s attention on we humans extending our capability beyond Earth/Moon space and into deep space. This is an essential capability in order to ultimately get to Mars, and a relatively short mission to a near-Earth asteroid is a logical first step in establishing a deep space human capability.”
And, Schweickart added, the excitement factor of such a mission would be off the charts. “Humans going into orbit around the Sun is pretty exciting!” said Schweickart, who piloted the lunar module during the Apollo 9 mission in 1969. “The Earth will be, for the first time to human eyes, a small blue dot.”
But not everyone agrees that an asteroid is the best destination for humans. Several of Schweickart’s Apollo compatriots, including Neil Armstrong, Jim Lovell and Gene Cernan, favor returning to the Moon and are concerned that President Obama’s directive is a “grounding of JFK’s space legacy.”
Compounding the issue is that NASA has not yet decided on a launch system capable of reaching deep space, much less started to build such a rocket.
Can NASA really go to an asteroid?
NASA Administrator Charlie Bolden has called a human mission to an asteroid “the hardest thing we can do.”
Excited by the challenge, NASA chief technology officer Bobby Braun said, “This is a risky, challenging mission. It’s the kind of mission that engineers will eat up.”
A human mission to an asteroid is a feat of technical prowess that might equal or exceed what it took for the US to reach the Moon in the 1960’s. Remember scientists who thought the moon lander might disappear into a “fluffy” lunar surface? That reflects our current understanding of asteroids: we don’t know how different asteroids are put together (rubble pile or solid surface?) and we certainly aren’t sure how to orbit and land on one.
“One of the things we need to work on is figuring out what you actually do when you get to an asteroid,” said Josh Hopkins from Lockheed Martin, who is the Principal Investigator for Advanced Human Exploration Missions. Hopkins leads a team of engineers who develop plans and concepts for a variety of future human exploration missions, including visits to asteroids. He and his team proposed the so-called “Plymouth Rock” mission to an asteroid (which we’ll discuss more in a subsequent article), and have been working on the Orion Multi-purpose Crew Vehicle (MPCV), which would be a key component of a human mission to an asteroid.
“How do you fly in formation with an asteroid that has a very weak gravitational field, so that other perturbations such as slight pressure from the Sun would affect your orbit,” Hopkins mused, in an interview with Universe Today. “How do you interact with an asteroid, especially if you don’t know exactly what its surface texture and composition is? How do you design anchors or hand-holds or tools that can dig into the surface?”
Hopkins said he and his team have been working on developing some technologies that are fairly “agnostic” about the asteroid – things that will work on a wide variety of asteroids, rather than being specific to an iron type- or carbonaceous-type asteroid.
Hypothetical astronaut mission to an asteroid. Credit: NASA Human Exploration Framework Team
A weak gravity field means astronauts probably couldn’t walk on some asteroids – they might just float away, so ideas include installing handholds or using tethers, bungees, nets or jetpacks. In order for a spaceship to stay in orbit, astronauts might have to “harpoon” the asteroid and tether it to the ship.
Hopkins said many of those types of technologies are being developed for and will be demonstrated on NASA’s OSIRIS-REx mission, the robotic sample return mission that NASA recently just selected for launch in 2016. “That mission is very complimentary to a future human mission to an asteroid,” Hopkins said.
Benefits
What benefits would a human asteroid mission provide?
“It would add to our body of knowledge about these interesting, and occasionally dangerous bodies,” said Schweickart, “and benefit our interest in protecting the Earth from asteroid impacts. So the human mission to a NEO is a very high priority in my personal list.”
Space shuttle astronaut Tom Jones says he thinks a mission to near Earth objects is a vital part of a planned human expansion into deep space. It would be an experiential stepping stone to Mars, and much more.
“Planning 6-month round trips to these ancient bodies will teach us a great deal about the early history of the solar system, how we can extract the water known to be present on certain asteroids, techniques for deflecting a future impact from an asteroid, and applying this deep space experience toward human Mars exploration,” Jones told Universe Today.
“Because an asteroid mission will not require a large, expensive lander, the cost might be comparable to a shorter, lunar mission, and NEO expeditions will certainly show we have set our sights beyond the Moon,” he said.
But Jones – and others – are concerned the Obama administration is not serious about such a mission and that the president’s rare mentions of a 2025 mission to a nearby asteroid has not led to firm NASA program plans, realistic milestones or adequate funding.
“I think 2025 is so far and so nebulous that this administration isn’t taking any responsibility for making it happen,” Jones said. “They are just going to let that slide off the table until somebody else takes over.”
Jones said he wouldn’t be surprised if nothing concrete happens with a NASA deep space mission until there is an administration change.
“The right course is to be more aggressive and say we want people out of Earth orbit in an Orion vehicle in 2020, so send them around the Moon to test out the ship, get them to the LaGrange points by 2020 and then you can start doing asteroid missions over the next few years,” Jones said. “Waiting for 2025 is just a political infinity in terms of making things happen.”
Jones said politics aside, it is certainly feasible to do all this by 2020. “That is nine years from now. My gosh, we are talking about getting a vehicle getting out of Earth orbit. If we can’t do that in nine years, we probably don’t have any hope of doing that in longer terms.”
Can NASA do such a mission? Will it happen? If so, how? Which asteroid should humans visit?
In a series of articles, we’ll take a closer look at the concepts and hurdles for a human mission to an asteroid and attempt to answer some of these questions.
