Seeker Blog

I think the survival of the human race deserves a long-term program to identify and deflect the inevitable dangerous near-earth objects. So, I’ve been looking for the March NASA report to Congress on the asteroid impact issue — just found it [PDF].

The NASA report doesn’t seem to favor the gravity space tug concept. This method appealed to me due to safety [doesn’t make the risk worse by fragmenting] and controllability [plenty of time to make course corrections]. But the study concludes that less than 1% of scenarios would suit the gravity tug approach — the report concludes it is too slow, and too inefficient at imparting the required velocity change.

Wait… I’m reading the critiques by Rusty Schweickart and Clark Chapman. According to these guys, the NASA report is a train wreck. Excerpt from Schweickart’s critique:

…This background technical report (the Final Report), held from public release, has nevertheless circulated through the NEO “community.” The analytic source of many of the objectionable conclusions contained in the Report to Congress are to be found in this document. The comments contained herein identify the most egregious technical errors in the Final Report but by no means reflect the full scope of errors scattered throughout the document. A full and exhaustive technical critique would be a major undertaking and is probably of limited value given the key errors addressed below.

The fact that NASA has submitted such a flawed report to the Congress and adamantly denied access to its antecedent technical analysis for review by the professional community is troubling, to understate the issue. The public safety issue of NEO impacts and the capability to prevent them by the use of space technology is one in which the value of public trust cannot be overemphasized. Absent NASA opening its full analysis to professional scrutiny and review, the public trust in the integrity and technical competence of NASA is in jeopardy.

The four technical errors identified below are then just a sampling of the problems associated with NASA’s handling of the Congressional mandate to address this issue. It is hoped that by openly publishing these and other shortcomings in the two NASA documents a serious review will be initiated by NASA and a revised and accurate report will be provided the public and the Congress.

The four errors Schweikart reviews are serious:

1. Failure to consider the size/frequency distribution of the NEOs which NASA would most likely be called on to divert from an Earth impact.

2. Failure to take into consideration, or even recognize, the existence and implications of multiple resonant returns and associated keyholes distributed along the deflection path (the Targeting issue).

3. The gravity tractor concept, which is independent of any specific spacecraft hardware, has erroneously been directly tied to the very expensive and technologically immature Prometheus spacecraft (or more generally, nuclear electric propulsion (NEP)).

4. The development and use of incorrect information on asteroid 144898 2004 VD17.

Schweikart and Chapman are both principles of the B612 Foundation, dedicated to practical solutions to the threat of asteroid impact. Their favored solution is based on a long and slow “dock and nudge” strategy. I like their approach — safe, precise/correctable and widely-useful technology. The B612 approach is completely dependent upon proper investment in the inventory and detection program [otherwise the action window may be too short]. As I understand it, this strategy will not handle either the extremely large, > 1km diameter, nor surprise bodies where we do not have decades to prevent the impact.

…Our preferred solution to deflecting an incoming near Earth asteroid (NEA), for reasons that are clarified below, is to rendezvous and “dock” with it at either its North or South Pole, realign the asteroid’s spin vector to a preferred direction and then push it (gently and for a long time) until we’ve changed its speed enough to miss the Earth. This scenario is very direct. It makes the key assumption, well supported by statistics and common sense that we will know of a pending impact many years ahead of time. The strange logic of NEA detection is that we will either know that an impact is pending several decades ahead of time, or that we will be hit by an asteroid we don’t know about with no warning at all! The critical importance of the detection program is that as you detect and track more and more NEAs you increase the former category and reduce the latter.

Because of the likely warning time of decades, we can utilize a deflection technique that is virtually universal, i.e., it does not depend strongly on the specific characteristics of the asteroid. A NEA-Tug will handle virtually any asteroid. The specifics of docking and attachment will vary slightly, but this is a minor challenge compared with the uncertainties and problems associated with many of the other possible deflection techniques. These alternatives will be discussed on another page.

An additional, but very important advantage of the NEA-Tug technique, it that all of the technologies and techniques needed to deflect an Earth-bound asteroid are also extremely useful for enabling both in situ scientific research and future asteroid resource exploitation. In addition, the power and propulsion technologies involved are key to future deep space missions. Given that asteroid deflection missions will be inherently few and far between, the fact that the technologies that enable it are also necessary for other key applications is of great importance.

It isn’t clear yet what the B612 team proposes for addressing the “big rock or short-time” case. The best resource for up-to-date info on impact threats is at JPL’s Near Earth Object Program. Most anything you wish to know can be found on the JPL site, e.g., what do those Palmero and Torino risk numbers mean?

…Most visitors to this web site will be primarily interested in the table presented on the Impact Risk Page. The rightmost two columns quantify the risk posed by the tabulated objects, using both the Torino Scale, which was designed primarily for public communication of impact risk, and the Palermo Technical Scale, which was designed for technical comparisons of impact risk. A Palermo Scale value less than zero and, in most cases, a Torino Scale value of zero, indicate a risk below the so-called background level (more info here), which is the average risk from the entire NEO population. To date, the risks posed by the potential impacts identified by Sentry have all been well below the background level, and hence, these events have been of academic or professional interest only, and not deserving of great public concern. Events with a Palermo Scale value greater than zero are expected to be very rare, but if one should be predicted, a Technical Review of the prediction would likely be requested from our colleagues in order to verify the calculations before the prediction is placed on the Risk Page.