In 2003 NASA commissioned a Science Definition Team (SDT) to study the threat posed by Near-Earth Objects (NEOs), to recommend solutions for efficiently detecting NEOs down to a much lower diameter than before, and to study techniques for mitigating an impending impact.
Subsequently, the United States Congress directed NASA to investigate ways to implement many of the SDT’s results. At this time Congress also set the goal of compiling a catalogue complete to 90% by 2020 of all NEOs larger than 140 meters in diameter. This 90%, 140 meter, 2020 set of goals was named in honor of George E. Brown, and is henceforth called the GEB requirement.
The SDT concluded that: the thermal infrared (~5 to ~11 microns) is the most efficient spectral regime for an efficient NEO search; that any IR aperture from about 50 to 100 centimeters is sufficient; and that locating a NEO-finding observatory in a Venus-like orbit (approximately a 0.7 AU semimajor axis) is ideal.
The SDT had to make assumptions about future advancements in detector technology and deep-space compatible processing power, and assumed that diffraction-limited optical systems with no chromatic aberrations were doable within the constraints of a flight mission.
Since then, NASA and its industrial partners, of which Ball Aerospace is one of many, have flown several deep-space missions, two of which are very relevant here — the infrared Spitzer Space Telescope (SST), and the recently launched Kepler mission, as discussed later.
In this paper we present a high reliability, credibly costed, high-heritage design that meets the GEB requirements for about $600M (USD). For no additional cost, this design will detect about 85% of all >100 meter diameter NEOs, about 70% of all >60 meter diameter NEOs, and about 50% of all >50 meter diameter NEOs.
These smaller NEOs constitute a newly recognized threat regime that cannot be efficiently detected from the ground.
…Recent work by Dr. Mark Boslough 4 shows that the impact physics of NEOs in the 30-100 meter range has been misunderstood due to a process he calls a Low-Altitude Airburst (LAA), which is a newly recognized threat regime that has been previously underestimated.
In an LAA event the main body of the NEO comes apart at high altitudes (~80 km to ~10 km), but the object’s mass and kinetic energy are conserved as a fast moving, loosely aggregated, collection of particles which entrain a column of air reaching the ground in what might be termed an “air hammer.” Dr. Boslough’s work shows that the “air hammer” from NEOs as small as 30 meters inflicts significant damage, as was seen in the 30-meter-class Tunguska event.
Dr. Boslough has also shown that an LAA from a ~100 meter diameter NEO melted sand into glass across a region about 10 km in diameter during Libyan Desert Glass impact ~35 million years ago. During this event the LAA’s fireball settled onto parts of Egypt and Libya for about a minute with temperatures approaching 5,000K. It’s hypersonic blast wave extended radially for about 100 kilometers.
Dr. Boslough has also shown that the interaction of the LAA with the ocean’s surface is much different from a large object’s strike, and that any ensuing tsunami is not yet well modelled.
Therefore any survey instrument capable of searching well below 140 meters is quite valuable.
Derating the estimate of the Tunguska object’s size from ~60 meters to today’s ~30 meters greatly decreases the impact interval from ~1,000 years to ~200 years.
Given that Tunguska happened 101 years ago, the expected time until the next impact is ~100 years….
