According to a new study from Brown University, it appears Ceres has more organic molecules on its surface than previously thought
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According to a new study from Brown University, it appears Ceres has more organic molecules on its surface than previously thought
The post Ceres Has Even More Organic Molecules on it Than Previously Thought appeared first on Universe Today.
Two new studies produced by the Dawn mission team have shown that the protoplanet may have once had an ocean, the remnants of which are likely in its interior today.
The post Wow! Asteroid/Dwarf Planet Ceres Once had an Ocean? appeared first on Universe Today.
A new study from the USC Viterbi School of Engineering, with the support of NASA, has found evidence of subsurface ice on Vesta.
The post Dawn Probe Finds Evidence of Subsurface Ice on Vesta appeared first on Universe Today.
A new study from a team of British and French physicists presents a concept for plasma thrusters that are both lighter and more energy-efficient.
The post New Way to Make Plasma Propulsion Lighter and More Efficient appeared first on Universe Today.
Researchers studying landslide on the surface of Ceres have noticed one with a distinctly Bart Simpson-like appearance.
The post Ceres Prank Lands Bart Simpson In Detention For Eternity appeared first on Universe Today.
A new study by an international team of scientists uses data provided by the Dawn probe to show that conditions favorable to life could exist on Ceres
The post Ceres Provides First Detection Of Life’s Building Blocks In Asteroid Belt appeared first on Universe Today.
Between the orbits of Mars and Jupiter lies the Solar System’s Main Asteroid Belt. Consisting of millions of objects that range in size from hundreds of kilometers in diameter (like Ceres and Vesta) to one kilometer or more, the Asteroid Belt has long been a source of fascination for astronomers. Initially, they wondered why the many objects that make it up did not come together to form a planet. But more recently, human beings have been eyeing the Asteroid Belt for other purposes.
Whereas most of our efforts are focused on research – in the hopes of shedding additional light on the history of the Solar System – others are looking to tap for its considerable wealth. With enough resources to last us indefinitely, there are many who want to begin mining it as soon as possible. Because of this, knowing exactly how long it would take for spaceships to get there and back is becoming a priority.
The distance between the Asteroid Belt and Earth varies considerably depending on where we measure to. Based on its average distance from the Sun, the distance between Earth and the edge of the Belt that is closest to it can be said to be between 1.2 to 2.2 AUs, or 179.5 and 329 million km (111.5 and 204.43 million mi).
However, at any given time, part of the Asteroid Belt will be on the opposite side of the Sun, relative to Earth. From this vantage point, the distance between Earth and the Asteroid Blt ranges from 3.2 and 4.2 AU – 478.7 to 628.3 million km (297.45 to 390.4 million mi). To put that in perspective, the distance between Earth and the Asteroid Belt ranges between being slightly more than the distance between the Earth and the Sun (1 AU), to being the same as the distance between Earth and Jupiter (4.2 AU) when they are at their closest.
But of course, for reasons of fuel economy and time, asteroid miners and exploration missions are not about to take the long way! As such, we can safely assume that the distance between Earth and the Asteroid Belt when they are at their closest is the only measurement worth considering.
The Asteroid Belt is so thinly populated that several unmanned spacecraft have been able to move through it on their way to the outer Solar System. In more recent years, missions to study larger Asteroid Belt objects have also used this to their advantage, navigating between the smaller objects to rendezvous with bodies like Ceres and Vesta. In fact, due to the low density of materials within the Belt, the odds of a probe running into an asteroid are now estimated at less than one in a billion.
The first spacecraft to make a journey through the asteroid belt was the Pioneer 10 spacecraft, which entered the region on July 16th, 1972 (a journey of 135 days). As part of its mission to Jupiter, the craft successfully navigated through the Belt and conducted a flyby of Jupiter (in December of 1973) before becoming the first spacecraft to achieve escape velocity from the Solar System.
At the time, there were concerns that the debris would pose a hazard to the Pioneer 10 space probe. But since that mission, 11 additional spacecraft have passed through the Asteroid Belt without incident. These included Pioneer 11, Voyager 1 and 2, Ulysses, Galileo, NEAR, Cassini, Stardust, New Horizons, the ESA’s Rosetta, and most recently, the Dawn spacecraft.
For the most part, these missions were part of missions to the outer Solar System, where opportunities to photograph and study asteroids were brief. Only the Dawn, NEAR and JAXA’s Hayabusa missions have studied asteroids for a protracted period in orbit and at the surface. Dawn explored Vesta from July 2011 to September 2012, and is currently orbiting Ceres (and sending back gravity data on the dwarf planet’s gravity) and is expected to remain there until 2017.
The fastest mission humanity has ever mounted was the New Horizons mission, which was launched from Earth on Jan. 19th, 2006. The mission began with a speedy launch aboard an Atlas V rocket, which accelerated it to a a speed of about 16.26 km per second (58,536 km/h; 36,373 mph). At this speed, the probe reached the Asteroid Belt by the following summer, and made a close approach to the tiny asteroid 132524 APL by June 13th, 2006 (145 days after launching).
However, even this pales in comparison to Voyager 1, which was launched on Sept. 5th, 1977 and reached the Asteroid Belt on Dec. 10th, 1977 – a total of 96 days. And then there was the Voyager 2 probe, which launched 15 days after Voyager 1 (on Sept. 20th), but still managed to arrive on the same date – which works out to a total travel time of 81 days.
Not bad as travel times go. At these speed, a spacecraft could make the trip to the Asteroid Belt, spend several weeks conducting research (or extracting ore), and then make it home in just over six months time. However, one has to take into account that in all these cases, the mission teams did not decelerate the probes to make a rendezvous with any asteroids.
Ergo, a mission to the Asteroid Belt would take longer as the craft would have to slow down to achieve orbital velocity. And they would also need some powerful engines of their own in order to make the trip home. This would drastically alter the size and weight of the spacecraft, which would inevitably mean it would be bigger, slower and a heck of a lot more expensive than anything we’ve sent so far.
Another possibility would be to use ionic propulsion (which is much more fuel efficient) and pick up a gravity assist by conducting a flyby of Mars – which is precisely what the Dawn mission did. However, even with a boost from Mars’ gravity, the Dawn mission still took over three years to reach the asteroid Vesta – launching on Sept. 27th, 2007, and arriving on July 16th, 2011, (a total of 3 years, 9 months, and 19 days). Not exactly good turnaround!
A number of possibilities exist that could drastically reduce both travel time and fuel consumption to the Asteroid Belt, many of which are currently being considered for a number of different mission proposals. One possibility is to use spacecraft equipped with nuclear engines, a concept which NASA has been exploring for decades.
In a Nuclear Thermal Propulsion (NTP) rocket, uranium or deuterium reactions are used to heat liquid hydrogen inside a reactor, turning it into ionized hydrogen gas (plasma), which is then channeled through a rocket nozzle to generate thrust. A Nuclear Electric Propulsion (NEP) rocket involves the same basic reactor converting its heat and energy into electrical energy, which would then power an electrical engine.
In both cases, the rocket would rely on nuclear fission or fusion to generates propulsion rather than chemical propellants, which has been the mainstay of NASA and all other space agencies to date. According to NASA estimates, the most sophisticated NTP concept would have a maximum specific impulse of 5000 seconds (50 kN·s/kg).
Using this engine, NASA scientists estimate that it would take a spaceship only 90 days to get to Mars when the planet was at “opposition” – i.e. as close as 55,000,000 km from Earth. Adjusted for a distance of 1.2 AUs, that means that a ship equipped with a NTP/NEC propulsion system could make the trip in about 293 days (about nine months and three weeks). A little slow, but not bad considering the technology exists.
Another proposed method of interstellar travel comes in the form of the Radio Frequency (RF) Resonant Cavity Thruster, also known as the EM Drive. Originally proposed in 2001 by Roger K. Shawyer, a UK scientist who started Satellite Propulsion Research Ltd (SPR) to bring it to fruition, this drive is built around the idea that electromagnetic microwave cavities can allow for the direct conversion of electrical energy to thrust.
According to calculations based on the NASA prototype (which yielded a power estimate of 0.4 N/kilowatt), a spacecraft equipped with the EM drive could make the trip to Mars in just ten days. Adjusted for a trip to the Asteroid Belt, so a spacecraft equipped with an EM drive would take an estimated 32.5 days to reach the Asteroid Belt.
Impressive, yes? But of course, that is based on a concept that has yet to be proven. So let’s turn to yet another radical proposal, which is to use ships equipped with an antimatter engine. Created in particle accelerators, antimatter is the most dense fuel you could possibly use. When atoms of matter meet atoms of antimatter, they annihilate each other, releasing an incredible amount of energy in the process.
According to the NASA Institute for Advanced Concepts (NIAC), which is researching the technology, it would take just 10 milligrams of antimatter to propel a human mission to Mars in 45 days. Based on this estimate, a craft equipped with an antimatter engine and roughly twice as much fuel could make the trip to the Asteroid Belt in roughly 147 days. But of course, the sheer cost of creating antimatter – combined with the fact that an engine based on these principles is still theoretical at this point – makes it a distant prospect.
Basically, getting to the Asteroid Belt takes quite a bit of time, at least when it comes to the concepts we currently have available. Using theoretical propulsion concepts, we are able to cut down on the travel time, but it will take some time (and lots of money) before those concepts are a reality. However, compared to many other proposed missions – such as to Europa and Enceladus – the travel time is shorter, and the dividends quite clear.
As already stated, there are enough resources – in the form of minerals and volatiles – in the Asteroid Belt to last us indefinitely. And, should we someday find a way to cost-effective way to send spacecraft there rapidly, we could tap that wealth and begin to usher in an age of post-scarcity! But as with so many other proposals and mission concepts, it looks like we’ll have to wait for the time being.
We have written many articles about the asteroid belt for Universe Today. Here’s Where Do Asteroids Come From?, Why the Asteroid Belt Doesn’t Threaten Spacecraft, and Why isn’t the Asteroid Belt a Planet?.
The post How Long Does it Take to get to the Asteroid Belt? appeared first on Universe Today.
We continue our “Definitive Guide to Terraforming” series with a look at another body in our Solar System – the dwarf planet Ceres. Like many moons in the outer Solar System, Ceres is a world of ice and rock, and is the largest body in the Asteroid Belt. Humans beings could one day call it home, but could its surface also be made “Earth-like”?
In the Solar System’s Main Asteroid Belt, there are literally millions of celestial bodies to be found. And while the majority of these range in size from tiny rocks to planetesimals, there are also a handful of bodies that contain a significant percentage of the mass of the entire Asteroid Belt. Of these, the dwarf planet Ceres is the largest, constituting of about a third of the mass of the belt and being the sixth-largest body in the inner Solar System by mass and volume.
In addition to its size, Ceres is the only body in the Asteroid Belt that has achieved hydrostatic equilibrium – a state where an object becomes rounded by the force of its own gravity. On top of all that, it is believed that this dwarf planet has an interior ocean, one which contains about one-tenth of all the water found in the Earth’s oceans. For this reason, the idea of colonizing Ceres someday has some appeal, as well as terraforming.
Ceres also has the distinction of being the only dwarf planet located within the orbit of Neptune. This is especially interesting considering the fact that in terms of size and composition, Ceres is quite similar to several Trans-Neptunian Objects (TNOs) – such as Pluto, Eris, Haumea, Makemake, and several other TNOs that are considered to be potential candidates for dwarf planets status.
Current estimates place Ceres’ mean radius at 473 km, and its mass at roughly 9.39 × 1020 kg (the equivalent of 0.00015 Earths or 0.0128 Moons). With this mass, Ceres comprises approximately a third of the estimated total mass of the Asteroid Belt (between 2.8 × 1021 and 3.2 × 1021 kg), which in turn is approximately 4% of the mass of the Moon.
The next largest objects are Vesta, Pallas and Hygiea, which have mean diameters of more than 400 km and masses of 2.6 x 1020 kg, 2.11 x 1020 kg, and 8.6 ×1019 kg respectively. The mass of Ceres is large enough to give it a nearly spherical shape, which makes it unique amongst objects and minor planets in the Asteroid Belt.
Ceres follows a slightly inclined and moderately eccentric orbit, ranging from 2.5577 AU (382.6 million km) from the Sun at perihelion and 2.9773 AU (445.4 million km) at aphelion. It has an orbital period of 1,680 Earth days (4.6 years) and takes 0.3781 Earth days (9 hours and 4 minutes) to complete a single rotation on its axis.
Based on its size and density (2.16 g/cm³), Ceres is believed to be differentiated between a rocky core and an icy mantle. Based on evidence provided by the Keck telescope in 2002, the mantle is estimated to be 100 km-thick, and contains up to 200 million cubic km of water, which is equivalent to about 10% of what is in Earth’s oceans, and more water than all the freshwater on Earth.
What’s more, infrared data on the surface also suggests that Ceres may have an ocean beneath its icy mantle. If true, it is possible that this ocean could harbor microbial extraterrestrial life, similar to what has been proposed about Mars, Titan, Europa and Enceladus. It has further been hypothesized that ejecta from Ceres could have sent microbes to Earth in the past.
Other possible surface constituents include iron-rich clay minerals (cronstedtite) and carbonate minerals (dolomite and siderite), which are common minerals in carbonaceous chondrite meteorites. The surface of Ceres is relatively warm, with the maximum temperature estimated to reach approximately 235 K (-38 °C, -36 °F) when the Sun is overhead.
Assuming the presence of sufficient antifreeze (such as ammonia), the water ice would become unstable at this temperature. Therefore, it is possible that Ceres may have a tenuous atmosphere caused by outgassing from water ice on the surface. The detection of significant amounts of hydroxide ions near Ceres’ north pole, which is a product of water vapor dissociation by ultraviolet solar radiation, is another indication of this.
However, it was not until early 2014 that several localized mid-latitude sources of water vapor were detected on Ceres. Possible mechanisms for the vapor release include sublimation from exposed surface ice (as with comets), cryovolcanic eruptions resulting from internal heat, and subsurface pressurization. The limited amount of data thus far suggests that the vaporization is more likely caused by sublimation from exposure to the Sun.
As with the moons of Jupiter and Saturn, terraforming Ceres would first require that the surface temperature be raised in order to sublimate its icy outer layer. This could be done by using orbital mirrors to focus sunlight onto the surface, by detonating thermonuclear devices on the surface, or colliding small asteroids harvested from the Main Belt onto the surface.
This would result in Ceres’ crust thawing and turning into a dense, water vapor-rich atmosphere. The orbital mirrors would once again come into play here, where they would be used to trigger photolysis and transform the water vapor into hydrogen and oxygen gas. While the hydrogen gas would be lost to space, the oxygen would remain closer to the surface.
Ammonia could also be harvested locally, since Ceres is believed to have plentiful deposits of ammonia-rich clay soils. With the introduction of specific strains of bacteria into the newly created atmospheres – such as the Nitrosomonas, Pseudomonas and Clostridium species – the sublimated ammonia could be converted into nitrites (NO²-) and then nitrogen gas. The end result would be an ocean world with seas that are 100 km in depth.
Another option would be to employ a process known as “paraterraforming” – where a world is enclosed (in whole or in part) in an artificial shell in order to transform its environment. In the case of Ceres moons, this could involve building large “Shell Worlds” to encase it, keeping the newly-created atmospheres inside long enough to effect long-term changes. Within this shell, Ceres temperature could be increased, UV lights would convert water vapor to oxygen gas, ammonia could be converted to nitrogen, and other elements could be added as needed.
In the same vein, a dome could be built over one or more of Ceres’ craters – particularly the Occator, Kerwan and Yalode craters – where the surface temperature could slowly be raised, and silicates and organic molecules could be introduced to create a terrestrial-like environment. Using water harvested from the surface, this land could be irrigated, oxygen gas could be processed, and nitrogen could be pumped in to act as a buffer gas.
The benefits of colonizing and (para)terraforming Ceres are numerous. For instance, it would take comparatively less energy to sublimate the surface than with the moons of Jupiter or Saturn. Under normal conditions, Ceres’ surface is warm enough (and it is likely there is sufficient ammonia) that its ices are unstable.
Also, Ceres appears from all accounts to be rich in resources, which include water ices and ammonia, and has a surface that is equivalent in total land area to Argentina. Also, the surface receives an estimated 150 W/m2 of solar irradiance at aphelion, one ninth that of Earth. This level of energy is high enough that solar-power facilities could run on its surface.
And being the largest body in the asteroid belt, Ceres could become the main base and transport hub for future asteroid mining infrastructure, allowing mineral resources to be transported to Mars, the Moon, and Earth. Its small escape velocity, combined with large amounts of water ice, means that it also could process rocket fuel, water and oxygen gas on site for ships going through and beyond the Asteroid Belt.
Despite the benefits of a colonized or transformed Ceres, there are also numerous challenges that would need to be addressed first. As always, they can be broken down into the following categories – Distance, Resources and Infrastructure, Hazards and Sustainability. For starters, Ceres and Earth are (on average) approximately 264,411,977 km apart, which is 1.7675 times the distance between the Earth and the Sun (and twice that between Earth and Mars).
Hence, any crewed mission to Ceres – which would involve the transport of both colonists, construction materials, and robotic workers – would take a considerable amount of time and involve a large expenditure in fuel. To put it in perspective, missions to Mars have taken anywhere from 150 to over 300 days, depending on how much fuel was expended. Since Ceres is roughly twice that distance, we can safely say that it would take a minimum of a year for a spacecraft to get there.
However, since these spacecraft would likely be several orders of magnitude heavier than anything previously flown to Mars – i.e. large enough to carry crews, supplies and heavy equipment – they would either need tremendous amounts of thrust to make the journey in the same amount of time, would have to spend much longer in transit, or would need more advanced propulsion systems altogether.
And while NASA currently has plans on the table to build laser-sail spacecraft that could make it Mars in three days times, these plans are not practical as far as colonization or terraforming are concerned. More than likely, advanced drive systems such as Nuclear-Thermal Propulsion (NTP) or a Fusion-drive system would be needed. And while certainly feasible, no such drive systems exist at this time.
Second, the process of building colonies on Ceres’ surface and/or orbital mirrors in orbit would require a huge commitment in material and financial resources. These could be harvested from the Asteroid Belt, but the process would be time-consuming, expensive, and require a large fleet of haulers and robotic miners. There would also need to be a string of bases between Earth and the Asteroid Belt in order to refuel and resupply these missions – i.e. a Lunar base, a permanent base on Mars, and most likely bases in the Asteroid Belt as well.
In terms of hazards, Ceres is not known to have a magnetic field, and would therefore not be shielded from cosmic rays or other forms of radiation. This would necessitate that any colonies on the surface either have significant radiation shielding, or that an orbital shield be put in place to deflect a significant amount of the radiation the planet receives. This latter idea further illustrates the problem of resource expenditure.
The extensive system of craters on Ceres attests to the fact that impactors would be a problem, requiring that they be monitored and redirected away from the planet. The surface gravity on Ceres is also quite low, being roughly 2.8% that on Earth (0.27 m/s2 vs. 9.8 m/s2). This would raise the issue of the long-term effects of near-weightlessness on the human body, which (like exposure to zero-g environments) would most likely involve loss of muscle mass, bone density, and damage to vital organs.
In terms of sustainability, terraforming Ceres presents a major problem. If the dwarf planet’s surface ice were to be sublimated, the result would be an ocean planet with depths of around 100 km. With a mean radius of less than 500 km, this means that about 21% of the planet’s diameter would consist of water. It is unlikely that such a planet (especially one with gravity as low as Ceres’) would be able to retain its oceans for long, and a significant amount of the water would likely be lost to space.
Under the circumstances, it seems like it would make more sense to colonize or paraterraform Ceres than to subject it to full terraforming. However, any such venture would have to wait upon the creation of a Lunar base, a settlement on Mars, and the development of more advanced propulsion technology. It was also require the creation of a fleet of deep-space ships and an army of construction and mining robots.
However, if and when such a colony were created, the resources of the Asteroid Belt would be at our disposal. Humanity would effectively enter an age of post-scarcity, and would be in a position to mount missions deeper into the Solar System (which could include colonizing the Jovian and Cronian systems, and maybe even the Trans-Neptunian region).
So for the time being, it looks like we’ll just have to be satisfied with developing faster spacecraft, returning to the Moon, and mounting crewed missions to Mars. As they say, baby steps!
We have written many interesting articles on terraforming here at Universe Today. Here’s The Definitive Guide to Terraforming, How Do We Terraforming Mars?, How Do We Terraform Venus?, How Do We Terraform the Moon?, How Do We Terraform Mercury?, How Do We Terraform Jupiter’s Moons?, and How Do We Terraform Saturn’s Moons?
For learn more about Ceres here, here are some articles on the many bright spots captured by the Dawn probe, and what they likely are. And here are some articles on the Asteroid Belt and Why it Isn’t a Planet.
NASA has selected Aerojet Rocketdyne to design and develop an advanced solar electric propulsion (SEP) system that will serve as a critical enabling technology for sending humans and robots on deep space exploration missions to cislunar space, asteroids and the Red Planet.
Under the 3 year, $67 million contract award, Aerojet Rocketdyne will develop the engineering development unit for an Advanced Electric Propulsion System (AEPS) with the potential for follow on flight units.
NASA hopes that the work will result in a 10 fold increase in “spaceflight transportation fuel efficiency compared to current chemical propulsion technology and more than double thrust capability compared to current electric propulsion systems.”
The SEP effort is based in part on NASA’s exploratory work on Hall ion thrusters which trap electrons in a magnetic field and uses them to ionize and accelerate the onboard xenon gas propellant to produce thrust much more efficiently than chemical thrusters.
The solar electric propulsion (SEP) system technology will afford benefits both to America’s commercial space and scientific space exploration capabilities.
For NASA, the SEP technology can be applied for expeditions to deep space such as NASA’s planned Asteroid Robotic Redirect Mission (ARRM) to snatch a boulder from the surface of an asteroid and return it to cislunar space during the 2020s, as well as to carry out the agency’s ambitious plans to send humans on a ‘Journey to Mars’ during the 2030s.
“Our plan right now is to flight test the higher power solar electric propulsion that Aerojet Rocketdyne will develop for us on the Asteroid Redirect Robotic Mission (ARRM), which is going to go out to an asteroid with a robotic system, grab a boulder off of an asteroid, and bring it back to a lunar orbit,” said Steve Jurczyk, associate administrator of NASA’s Space Technology Mission Directorate (STMD) in Washington, at a media briefing.
ARRM would launch around 2020 or 2021. Astronauts would blast off several years later in NASA’s Orion crew capsule in 2025 after the robotic probes travels back to lunar orbit.
For industry, electric propulsion is used increasingly to maneuver thrusters in Earth orbiting commercial satellites.
“Through this contract, NASA will be developing advanced electric propulsion elements for initial spaceflight applications, which will pave the way for an advanced solar electric propulsion demonstration mission by the end of the decade,” says Jurczyk.
“Development of this technology will advance our future in-space transportation capability for a variety of NASA deep space human and robotic exploration missions, as well as private commercial space missions.”
The starting point is NASA’s development and technology readiness testing of a prototype 13-kilowatt Hall thruster and power processing unit at NASA’s Glenn Research Center in Cleveland.
Under the contract award Aerojet Rocketdyne aims to carry out the industrial development of “high-power solar electric propulsion into a flight-qualified system.”
They will develop, build, test and deliver “an integrated electric propulsion system consisting of a thruster, power processing unit (PPU), low-pressure xenon flow controller, and electrical harness,” as an engineering development unit.
This engineering development unit serves as the basis for producing commercial flight units.
If successful, NASA has an option to purchase up to four integrated flight units for actual space missions. Engineers from NASA Glenn and the Jet Propulsion Laboratory (JPL) will provide technical support.
Solar electric ion propulsion is already being used in NASA’s hugely successful Dawn asteroid orbiter mission.
Dawn was launched in 2007. It orbited and surveyed Vesta in 2011 and 2012 and then traveled outward to Ceres.
Dawn arrived at dwarf planet Ceres in March 2015 and is currently conducting breakthrough science at its lowest planned science mapping orbit.
A key part of the Journey to Mars, NASA will be sending cargo missions to the Red Planet to pave the way for human expeditions with the Orion crew module and Space Launch System.
Aerojet Rocketdyne states that “Solar Electric Propulsion (SEP) systems have demonstrated the ability to reduce the mission cost for NASA Human Exploration cargo missions by more than 50 percent through the use of existing flight-proven SEP systems.”
“Using a SEP tug for cargo delivery, combined with NASA’s Space Launch System and the Orion crew module, provides an affordable path for deep space exploration,” said Aerojet Rocketdyne Vice President, Space and Launch Systems, Julie Van Kleeck.
Another near term application of high power solar electric propulsion could be for NASA’s proposed Mars 2022 telecom orbiter, said Bryan Smith, director of the Space Flight Systems Directorate at NASA’s Glenn Research Center in Cleveland, at the media briefing.
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
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