Projectile space launch - the use of ground-based accelerators to help put payloads into orbit.
Putting things into orbit is expensive. The recurring engineering costs required to orbit payloads using projectile space launchers should be far lower than those for rocketry, perhaps by an order of magnitude. 1 The global environmental impact might be lower as well. For example, by avoiding or minimizing rocket firings in the atmosphere, it should be possible to launch lots of cargo into orbit with much less degradation of the atmosphere by pollutants such as soot, which has high global warming potential (GWP).2,3
Project Persephone's focus on aid and development projects in equatorial alpine regions is strongly motivated by the likelihood that these regions can be made ideal for projectile space launch. Of course, such regions also tend to be relatively undeveloped and energy-poor. Space launch tends to require expensive labor (recurring engineering costs?) from developed countries, and it's also quite energy-intensive. However, some schemes for projectile launch, such as the ram accelerator, could require relatively little energy per unit of mass orbited, and only very simple infrastructure requiring relatively little expert operation and maintenance.
Communities in alpine equatorial regions might be able to provide most of the basic material and energy for launch. In particular, the ram accelerator shows promise for providing high accelerations from tubes that, with appropriate engineering4 might be made from materials far less exotic than many of those seen in high-performance aerospace applications. The energy from the byproducts of sustainable forestry, and using off-peak electricity surpluses from small hydro, wind power? and geothermal energy might be more than adequate. If the crater of a dormant or extinct volcano considered as a launch point contains a caldera lake, the same drilling equipment used for tapping geothermal sources might be used to bore a "pilot tunnel" from the crater to the base, for small hydro. Development of such energy sources in candidate regions for local community use and for supplying their neighboring communities, should take precedence as a Project focus. The Project would help supply the needed equipment and expertise in exchange for promises of an adequate share of energy, if and when the time comes for projectile launch development.
There has been research, even relatively recently, on boosting partly air-breathing spacecraft up to supersonic speeds along more-or-less horizontal tracks, with a view toward eventually hosting man-rated launchers5. However, Project Persephone doesn't aim for manned launch, which is inevitably expensive. Instead of relatively low horizontal acceleration as a prelude to hypersonic aerodynamic stages, it looks instead to sites for high-angle, very high acceleration launch from mountain slopes, particularly those of extinct or dormant stratovolcanoes near the equator, obviating the need for complex air-breathing propulsion stages.
A common objection to projectile space launch is that nothing of any complexity could survive it -- at best, it's thought that only bulk materials might be shipped. However, complex unpiloted aerial vehicles have been designed that fold into a package formed as a standard 155 mm artillery round, demonstrating in tests that they can function after being subjected to 12,000 g accelerations.6 The payloads required for telebotic construction of exovivaria can almost certainly be engineered to survive similar launch stresses, if necessary.
Another common objection to projectile space launch is that the vehicles would simply disintegrate in the lower atmosphere. However, it's been estimated that even low-mass projectiles exiting an accelerator at sea level could survive transit of the atmosphere with less than half of their mass devoted to cooling or ablative shielding.7. For larger projectiles at higher altitudes, the mass requirement for thermal protection has been estimated as low as 1% of total mass accelerated.
A more serious objection to projectile space launch from the Earth's surface is environmental: atmospheric shock waves. The muzzle shock wave from light gas gun launches at Lawrence Livermore was strong enough to kill nearby plant life. (Ref needed) Endangered animal species, such the Andean Condor, might be displaced from some habitats, and significantly disturbed in others. Sonic booms from the projectile might be very alarming and stressful to people even hundreds of kilometers away. Careful siting, timing and advance warning might ameliorate the problem to some extent. With an exit point from a volcano crater, perhaps a significant portion of the shock could be deflected upward; higher launch altitudes would tend to reduce shock intensity; and higher altitudes also correlate with more remote locations, with fewer human and animal inhabitants. Sonic shock environmental impact is an important criterion for narrowing the choice of sites, and will likely be an ongoing research topic even after likely sites are chosen for preliminary development.
- The Space Review, "Space and (or versus) the environment", http://thespacereview.com/article/1395/1
- "Studies on Ground Based Accelerators", Gerry Flanagan, 2011
1 "Ground-based, hypervelocity accelerators for low-cost delivery of large numbers of small, high-g tolerant payloads to LEO are a near-term technology that can provide significant payoff for a relatively small technology investment." NASA, April 2012. Launch Propulsion Systems Roadmap: Technology Area 01, p.2 ⇑
3 Geophysical Research Letters, v.37, 2010, "Potential climate impact of black carbon emitted by rockets", Martin Ross, Michael Mills, Darin Toohey, doi:10.1029/2010GL044548 ⇑
4 "Gasdynamic Operation of Baffled Tube Ram Accelerator in Highly Energetic Mixtures", A.J. Higgins, C. Knowlen, C.B. Kiyanda, Submitted to: 20th International Colloquium on the Dynamics of Explosions and Reactive Systems. http://www.galcit.caltech.edu/~jeshep/icders/cd-rom/EXTABS/178_20TH.PDF ⇑
5 "First Stage of a Highly Reliable Reusable Launch System", Kurt J. Kloesel, Jonathan B. Pickrel, Emily L. Sayles, Michael Wright, Darin Marriott, Leo Holland, Stephen Kuznetsov, AIAA 2009-6805. http://pdf.aiaa.org/preview/CDReadyMSPACE09_2074/PV2009_6805.pdf ⇑