by Paul Gilster | Dec 5, 2012 | Missions |
One rainy night in the mid-1980s I found myself in a small motel in the Cumberlands, having driven most of the day after a meeting and reaching Newport, TN before I decided to land for the night. It’s funny what you remember, but small details of that trip stick with me. I remember the nicking of the wiper blades as I approached Newport, the looming shapes of the mountains in the dark, and most of all the fact that I was thinking about an interstellar mission. I was working on a short story that grew out of the Voyager mission and the experience of those who controlled it.
After a late dinner at a restaurant near the motel, I asked myself what it would be like to be involved in a truly long-term mission. Suppose we develop the technologies to get a probe up to a few percent of the speed of light. If we send out a flyby mission to the nearest stars, we’re talking about a couple of centuries of flight time, or maybe a bit less. It’s inevitable, then, that a mission like this would be handed off from one generation to the next. Clearly the people who worked the stellar encounter would have been born and matured long after the mission left.
My story involved a man who worked on such a mission as the probe closed within a year of its encounter with Epsilon Indi, a man who learned that, although he was only in his 40s, he was dying and wouldn’t see the probe reach its destination. Back in those days the many avenues of exoplanet investigation weren’t yet clear and we had no good data on planets around other stars, so the big question was whether the probe would find planets around the star or not. But the larger issue was the human perspective on time and commitment even in the face of mortality.
I think about things like that every time I read the latest news from Voyager. The most recent information involves a so-called ‘magnetic highway’ and the behavior of charged particles in the heliosheath as Voyager 1 pushes closer to interstellar space. I can check this morning to see that the spacecraft is now 18,462,802,513 kilometers from the Earth, which works out to a one-way light time of just a bit over 17 hours. Voyager 1 was launched on the 5th of September, 1977, but it’s still a live presence that should keep sending back data perhaps for a decade.
There are surely people working around the periphery of the ongoing Voyager missions who weren’t born when they were launched. What would it be like for a civilization like ours to watch a true interstellar mission over the course of lifetimes, a deep space presence that, no matter what else we found ourselves doing would periodically galvanize the attention, reminding all of us that it was still out there, a heart still beating, a mind (human or artificial) still sending back data. There is something grand in that notion that calls up not just physics and astronomy but archaeology, the recovery of history and perspective, of humanity considered over deep time.
But of course when you’re working a mission, you have very practical work to do. Stamatios Krimigis (JHU/APL) is principal investigator of Voyager’s Low-Energy Charged Particle (LECP) instrument. Voyager 1 crossed the so-called ‘termination shock’ in late 2004 and moved into the heliosheath, where the solar wind has slowed and become turbulent. For a time the solar wind dropped to zero and the intensity of the magnetic field began to increase. I sense the practical scientist as well as a bit of the philosopher in Krimigis as he describes all this:
“The solar wind measurements speak to the unique abilities of the LECP detector, designed at APL nearly four decades ago. Where a device with no moving parts would have been safer – lessening the chance a part would break in space – our team took the risk to include a stepper motor that rotates the instrument 45 degrees every 192 seconds, allowing it to gather data in all directions and pick up something as dynamic as the solar wind. A device designed to work for 500,000 ‘steps’ and four years has been working for 35 years and well past 6 million steps.”
A four year design still functioning after 35 is a tribute to the engineering that conceived it and a reminder of the timescales that missions into much deeper space will one day have to reckon with. As to Voyager, has it entered a new region of space? This JHU/APL news release gives useful background: The LECP instrument has seen sudden increases in cosmic rays and decreases in low-energy particles, a varying scenario that has yet to settle down. Krimigis and team are saying that Voyager may be in a new region but not yet in true interstellar space.
Image: This artist’s concept shows plasma flows around NASA’s Voyager 1 spacecraft as it gets close to entering interstellar space. Voyager 1’s Low-Energy Charged Particle instrument detects the speed of the wind of plasma, or hot ionized gas, streaming off the sun. It detected the slowing of this wind – also known as the solar wind – to zero outward velocity in a region called the stagnation region. Scientists had expected that the solar wind would turn the corner as it felt the pressure of the interstellar magnetic field and the interstellar wind flow. But that did not happen, so scientists don’t know what to expect once Voyager actually crosses the heliopause. Credit: NASA/JPL-Caltech/The Johns Hopkins University Applied Physics Laboratory.
The term ‘magnetic highway’ comes up because in this region low-energy particles from inside the heliosphere are flowing out while higher-energy particles are flowing in — the Sun’s magnetic field lines are connected to interstellar magnetic field lines. While charged particles bounced in all directions before Voyager 1 entered this region, as if firmly contained by the surrounding heliosphere, they’re now much more directional. Krimigis again:
“If we were judging by the charged-particle data alone, I would have thought we were outside the heliosphere. In fact, our instrument has seen the low-energy particles taking the exit ramp toward interstellar space. But we need to look at what all the instruments are telling us and only time will tell whether our interpretations about this frontier are correct. One thing is certain - none of the theoretical models predicted any of Voyager’s observations over the past 10 years, so there is no guidance on what to expect.”
I suppose it was the ‘magnetic highway’ metaphor that brought back my night drive through the Cumberlands and all the musing about interstellar missions at a time when Voyager 2 had not yet reached Neptune (and Voyager 2, by the way, shows no signs of reaching the magnetic highway at a distance of about 15 billion kilometers from Earth). Voyager project scientist Ed Stone (Caltech), as venerable a figure as they come in the Voyager pantheon, thinks true interstellar space is a few months to a couple of years away for the farthest Voyager.
We’ll lose something priceless when the Voyagers finally go silent, but New Horizons is still robust and that gives me hope. I think we need a continuing voice from the deep dark to remind us that our nature is to explore even if human lifetimes fade to insignificance against the starry backdrop that bore us. Daily work is the thing, and to work for what Tennyson called ‘the long result’ is the best work there is, whether we’re there to see the end of the mission or not.
by Paul Gilster | Dec 4, 2012 | Advanced Rocketry |
Richard Obousy, a familiar face on Centauri Dreams, is president and primary propulsion senior scientist for Icarus Interstellar, whose portfolio includes Project Icarus, the redesign of the Project Daedalus starship. Dr. Obousy is just back from the latest Advanced Space Propulsion Workshop and, as he did for the 2010 ASPW, he now offers his take on the event. Although I missed this ASPW, I’ll be back in Huntsville soon for an upcoming conference, and I heartily second what Richard has to say about that Saturn V at the US Space and Rocket Center. It’s not to be missed.
by Richard Obousy
The 2012 Advanced Space Propulsion Workshop (ASPW) was held over three days at the US Space and Rocket Center in Huntsville, Alabama running from Tuesday 27th November to Thursday 29th November. The conference was sponsored by the Game Changing Development Program under NASA’s Space Technology Program and the Office of the Chief Technologist at NASA Marshall Space Flight Center.
This was the 19th cycle of the workshop, with the first workshop convening in 1990. Owing mainly to NASA budget cuts, the conference ceased being annual after the 16th workshop in April 2005.
ASPW focuses principally on early-stage propulsion research, in the Technology Readiness Level (TRL) 1-2 range. Presentations were loosely grouped by topic, with subjects including Advanced Electric Propulsion, Propellantless Propulsion, Advanced Launch Systems, Nuclear Propulsion, and Micropropulsion.
Image: Saturn V model at the US Space and Rocket Center with Icarus Interstellar Directors Robert Freeland, Richard Obousy and Bill Cress on a particularly chilly Huntsville afternoon.
Icarus Interstellar had seven team members in attendance including myself and Directors Robert Freeland, Andreas Tziolas and Bill Cress, also researchers Tabitha Smith (Bifrost), Milos Stanic (Project Icarus) and Rob Adams (Project Icarus). Being a ‘virtual’ team we rarely have the chance to see each other face to face, so it was fantastic to have the opportunity to all meet up in the same room. In addition to attending the workshop, the Icarus Interstellar team also held private meetings where we were able to discuss a number of organizational and project matters.
Image: Five of the seven Icarus Interstellar team members attending ASPW. From left to right, Andreas Tziolas, Richard Obousy, Bill Cress, Milos Stanic, Rob Adams.
While the presentations are typically the foci of workshops like this, the networking value of the conference cannot be understated. We had the opportunity to expose our team and our mission to some of the most adept propulsion scientists in the country and solicit feedback and make new friends. I had the privilege of attending the 2010 ASPW, and back then I found that few had heard of Icarus Interstellar. However this year our work was well known, and we even noted several citations to our work from other conference presenters. For me, the fact that our hard (and volunteer) work is getting us noticed within this community speaks volumes regarding the dedication and commitment of the team.
There were a number of highlights of the event for me. One was having the pleasure to engage with Professor Friedwardt Winterberg, an American theoretical physicist who was the creative force behind the Daedalus engine. He collaborated with Alan Bond and the Project Daedalus team back in the 1970s to create the “Winterberg Daedalus Class Magnetic Compression Reaction Chamber”, an internal/external hybrid inertial confinement fusion pulsed propulsion design. Although this design is now known to have some fundamental flaws, it was arguably the most visionary interstellar propulsion design in its time.
Image: Andreas Tziolas and Richard Obousy talking with the inspiration for the Daedalus engine, physicist Friedwardt Winterberg.
Another highlight for me was a tour of the Marshall Space Flight Center situated in the Army’s Redstone Arsenal base. There I was thrilled to see a Marx generator being prepared for study of plasma instabilities under fusion conditions. The device is able to discharge a 1 TW pulse after charging a large number of capacitor banks.
One final highlight was the US Space and Rocket Center just a short walk from the ASPW workshop. The museum housed one of the three remaining Saturn V rockets on public display and was designated a national historic landmark by the National Park Service in 1987. Seeing the rocket for me is always a bittersweet experience. It’s a reminder of a tremendous era for our space exploration, when Americans came together to undertake one of the most profound missions of exploration in all of history. It’s also a sad reminder that it’s been almost forty years since we last stepped foot on the moon, with no firm plans to return in the foreseeable future. I hope that workshops like ASPW cement the foundations for a brave new era in space exploration, one that I live to see.
by Paul Gilster | Dec 3, 2012 | Advanced Rocketry |
The news from Reaction Engines Ltd. about its air-breathing rocket engine SABRE is interesting not only for its implications in near-term space development, but also for its pedigree. Reaction Engines grew out of British work on a single-stage-to-orbit concept called HOTOL ((Horizontal Take-Off and Landing) that was being developed by Rolls Royce and British Aerospace in the 1980s. Initially backed by the British government, HOTOL lost its funding in 1988, prompting Alan Bond’s decision to form the new company, which would continue the work with private funds.
The name Alan Bond should ring many bells for Centauri Dreams readers. Bond was a key player in and leading author of the report on the British Interplanetary Society’s Project Daedalus, the ambitious 1970s attempt to design a starship based on fusion propulsion. One thing the extensive Daedalus effort made clear was that a future attempt to reach the stars could only take place within the context of a Solar System-wide infrastructure, one that would have the ability to mine the atmospheres of the outer planets for the needed helium-3 and other resources. It’s no surprise, then, that Bond’s attention should now be on that infrastructure and how to build it.
Image: Reaction Engines’ Alan Bond, whose company’s recent tests promise single-stage-to-orbit at drastically reduced costs.
For one craft SABRE is intended to power is a reusable spaceplane called Skylon that would reach orbit in a single stage, lowering the cost per kilogram of payload substantially, perhaps to as little as $1000 or less. As presented by Reaction Engines, Skylon is anything but another Space Shuttle. It would take off from a conventional runway, accelerating to Mach 5.4 at 26 kilometers altitude before switching its engines over to internal liquid oxygen mode to take the craft to low-Earth orbit.
The project’s backers say they can carry up to 15 tonnes into orbit aboard the unpiloted craft, a payload that could also, using a habitation module, be comprised of up to 30 astronauts in a single launch vehicle. Upon delivery of its cargo or complement of astronauts, the vehicle would re-enter the Earth’s atmosphere and land back at the runway, undergoing inspection and any needed maintenance before, within two days, being returned to the flight line. If Skylon can live up to this ambitious scenario, then it will have given us what the Space Shuttle promised — reusability with quick turnaround — in a far more flexible and much less expensive design.
Much comes down, as you can imagine, to the SABRE engine. The acronym stands for Synergistic Air-Breathing Rocket Engine, a design that combines a turbo-compressor with an air pre-cooler that at high speeds can cool hot compressed air that will then be fed into the rocket combustion chamber, where liquid hydrogen will form the other part of the mixture to be ignited. The pre-cooler technology is the key. It allows the incoming airstream to be cooled from over 1000 degrees C to minus 150 C in less than 1/100th of a second without any frost blockage.
SABRE thus works initially in air-breathing mode, using the atmosphere as its source of oxygen for burning with the liquid hydrogen in the rocket combustion chamber. Once above the atmosphere, the craft makes the transition to conventional on-board liquid oxygen. The dual approach means that a vehicle like Sylon could save over 250 tons of on-board oxidant — no huge first stage that has to be jettisoned as soon as the oxidant is used up . The pre-cooler work is critical because in its air-breathing mode, SABRE has to compress the air to 140 atmospheres before injecting it into the combustion chamber. Without the new pre-cooler technology, that would raise the air temperatures high enough to melt engine materials.
Recent tests on SABRE involving over 100 test runs at the Reaction Engines facility in Oxfordshire have demonstrated the workability of the concept in the eyes of the European Space Agency, which has been funding part of the work. This Reaction Engines news release quotes ESA’s evaluation: “The pre-cooler test objectives have all been successfully met and ESA are satisfied that the tests demonstrate the technology required for the SABRE engine development.” The successful pre-cooler testing should allow the release of additional funding for the Skylon project from the British government according to an April 2011 agreement.
As for Alan Bond, he’s convinced Reaction Engines has proven its point:
“These successful tests represent a fundamental breakthrough in propulsion technology. Reaction Engines’ lightweight heat exchangers are going to force a radical re-think of the design of the underlying thermodynamic cycles of aerospace engines. These new cycles will open up completely different operational characteristics such as high Mach cruise and low cost, re-usable space access, as the European Space Agency’s validation of Reaction Engines’ SABRE engine has confirmed. The REL team has been trying to solve this problem for over 30 years and we’ve finally done it. Innovation doesn’t happen overnight. Independent experts have confirmed that the full engine can now be demonstrated. The SABRE engine has the potential to revolutionise our lives in the 21st century in the way the jet engine did in the 20th Century. This is the proudest moment of my life.”
You have to imagine that amidst that pride there is a bit of the old Daedalus excitement lingering in Bond’s work with Skylon, given that lowering launch costs by more than ten times is a necessary first step toward the infrastructure he foresaw as far back as the 1970s, when the Daedalus designers crunched numbers and sketched ideas at the Mason’s Arms pub on Maddox Street in London. But while Daedalus was speculative and, for its time, science fictional in its ambitions, Reaction Engines is now working with a design that could have a payoff in the not so distant future. We build out an infrastructure one step at a time, but the first step is to get into position. Cheap access to low-Earth orbit opens up scenarios that may one day take us far beyond our planet.
