2011 AG5 Deflection and Decision Analysis
- Introduction:
While unable to perform a general analysis of mission design options for a potential 2011 AG5 deflection, I we have examined, within the limits of my capability, two specific mission scenarios. These point designs look at two boundary cases which, if either is only marginally within current capability or seemingly beyond current capability, suggest that immediate professional analysis is indicated.
1)Scenario 1. A direct impact deflection campaign of 2011 AG5 initiated immediately following a keyhole encounter in Feb 2023. This scenario assumes an ASAP deployment of an observer spacecraft [1](S/C) following the determination of a 2023 keyhole passage and a completed KI deflection by 2030.
2)Scenario 2. An immediate commitment to a keyhole deflection campaign for 2011 AG5. Due to the size of the 2023 keyhole and the limited time available a campaign comprised of an observer S/C and KI impactor S/C are required.
The conclusions below assume the deflection requirements presented in the Analysis, Assumptions and Comments section (below) and are both limited and approximate. It is the best that Iam able to do with my own very modest capability and limited support. Nevertheless I believe it is representative enough of the actual situation that professional review and independent analysis is warranted. There are many assumptions and estimates incorporated in this analysis, which, while based on both experience and limited available information, may have led me to be overly concerned. For this reason I present it here for your review and potential action
The KI mission design options I use are selected from the “KI trajectory design summary” (Table 1) (Note: trajectory computations were provided by independent consultant Dan Adamo, to whom Iam very grateful). The key variables in this table are the departure and arrival dates (for the KI mission), the C3 required, and the effective ΔV achieved at impact with the NEO (derived from columns B, C, D, and I respectively). The launch vehicle performance values used in my conclusion are based on the online performance for current launch vehicles found on the Silverbird Astronautics site at
- Summary:
Scenario 1.
Based on the launch of an observer S/C in 2023 it is assumed that a KI impact can be achieved no earlier than ~Nov 2029. The most attractive KI intercept mission (Line# 27, Table 1) would result in a completed deflection impact on 27 Nov 2029. The relevant information from that table is:
Departure date Arrival date C3 Effective Vimp Impactor Mreq
2029-03-12 2029-11-27 6.15 -7.967 km/s 10,000 kg
Notes: C3 units = km2/sec2. Effective Vimp is the component of the impactor velocity parallel to the NEO velocity vector. Impactor Mreq is the mass of the KI impactor required to achieve the total impulse parallel to the NEO velocity to produce the targeted Earth miss distance.
The impactor mass required (Mreq) is based on an assumed ΔV requirement of 1e-2 m/sec for a1Re NEO displacement (Fig. 1), a 4 Re targeted miss distance from the Earth center, and a momentum multiplier(β) of 2.0. The resultant required effective total impulse is therefore 8e7 kg-m/sec. (see Analysis, Assumptions and Comments below)
The published available performance capability of the Atlas-V Heavy, Delta-IV Heavy, and the proposed Falcon 9 Heavy are:
Atlas V Heavy w/DEC & long fairing
Launch Site: Cape Canaveral / KSC
Escape Trajectory: C3 = 6 km2/s2, 16 deg
Estimated Payload: 7840 kg
95% Confidence Interval: 6486 - 9510 kg
Delta IV Heavy w/long fairing
Launch Site: Cape Canaveral / KSC
Escape Trajectory: C3 = 6 km2/s2, 16 deg
Estimated Payload: 8905 kg
95% Confidence Interval: 7649 - 10259 kg
Falcon Heavy w/long fairing
Launch Site: Cape Canaveral / KSC
Escape Trajectory: C3 = 6 km2/s2, 16 deg
Estimated Payload: 13585 kg
95% Confidence Interval: 11060 - 16614 kg
It therefore appears that the direct deflection option for 2011 AG5, initiated immediately post-2023 close encounter, could not be successfully accomplished using the most capable currently available launch vehicles. Assuming the availability of the proposed Falcon 9 Heavy launch vehicle the post-2023 direct deflection mission appears feasible with a slight payload margin.
Scenario 2.
The 2023 keyhole, through which 2011 AG5 must pass in order for there to be an Earth impact in 2040 is approximately 100 km wide (estimate by JPL). The total impulse required to avoid this keyhole (assuming AG5 passes through its center) is approximately an order of magnitude greater than the capability of a 1 MT gravity tractor towing a NEO for 1 year, even with “generous” performance assumptions. Therefore given the time criticality for a keyhole deflection the analysis below assumes the need for a deflection campaign comprised of an observer S/C and a small kinetic impactor S/C combined.
For an immediate initiation of a keyhole deflection campaign it is assumed that the earliest date by which a completed KI impact can be accomplished is 2019[2]. This assumes an ASAP launch and rendezvous of an observer S/C with the NEO, a precise determination of whether or not the trajectory will result in a keyhole passage, and (in the unlikely event it so appears) the launch and intercept of the NEO by a KI impactor. Assuming 5 years from the present for the observer S/C to precisely determine the NEO orbit the KI impactor S/C would have only 2 years to complete its launch, intercept and deflection of the NEO. This is clearly an extremely tight timeline.
The impactor mass required (Mreq) is based on an assumed ΔV requirement of 5e-4 m/sec for a 1Re NEO displacement (Fig. 1), a 4 Re targeted miss distance from the Earth center, and a β of 2.0. The resultant required effective total impulse is therefore 4e6 kg-m/sec. (see Analysis, Assumptions and Comments below)
This effective total impulse delivered (based on comparable analysis done for the direct deflection analysis) appears well within the capability of existing launch vehicles. Nevertheless the execution planning timeline to accomplish a deflection by 2019 is tight. Furthermore a decision to immediately commit to this deflection campaign would have to be made based on the current probability of keyhole passage of 1 in 625.
Nevertheless if a decision to deflect were deferred until after the next likely tracking apparition in Sept 2013 (personal communication with Dave Tholen) essentially 2 years would be removed from the timeline. The “benefit” associated with the “cost” of this 2 year penalty would be (in the unlikely assumption that AG5 is indeed headed for the keyhole) an increased impact probability of perhaps 1 in 300 (very approximate). The ability to conduct the assumed observer + KI deflection campaign beginning in late 2013 seems marginal. Only detailed analysis of this option would determine its feasibility.
Conclusion:
To assure that asteroid 2011 AG5 does not impact Earth in Feb 2040, given the unlikely assumption that it is on a trajectory to do so (current probability 1 in 625), either a near-term commitment to a keyhole deflection must be made or a choice must be made to “wait and see” if the NEO passes through the keyhole at which time an immediate commitment must be made to a direct deflection campaign.
A direct deflection campaign, initiated immediately post-keyhole passage appears beyond the capability of existing launch vehicles.
A keyhole deflection campaign, if initiated immediately appears to be feasible. If delayed until additional tracking data becomes available, however, it appears marginal.
If no decision is made in the near future the “effective” decision is to accept a 1 in 625 chance a 100 megaton impact in 2040.
Analysis, Assumptions, and Comments:
Scenario 1. Direct Impact analysis:
[Comment: Given the evident challenge of completing a keyhole deflection in the 11 years to the 2023 keyhole passage (or 9 years if delayed till after the next apparition), size of the NEO orbit, and likely requirement for a full deflection campaign (i.e. both t-GT/observer and KI missions) given the ~100 km size of the keyhole, I first consider the elements of a post-2023, “direct” deflection, assuming one is required.]
Assumptions, definition of terms, comments:
2011 AG5 (hereafter AG5) key parameters :
AG5 mass = 4e9 kg
Diameter ~ 140 meters
Orbital period (post keyhole) = 1.7 years
Synodic period = 2.43 years
Deflection effective ΔV required in 2030 for 1 Re displacement by 2040 impact ~ 1 cm/sec (approximation based on ΔV vs date for 2004 MN4, 2004 VD17; Milani, et al, Fig. 1)
[note: “effective ΔV” or “effective total impulse” refer to the component of the intercept ΔV (and impulse) parallel to the NEO velocity vector.]
Net effective total impulse required (1 Re displacement) ~ 4e7 kg-m/sec
Net effective total impulse required (4 Re displacement) ~1.6e8 kg-m/sec
Momentum multiplier (β) = 2 (conservative assumption)
Net effective total impulse required for KI ~ 8e7 kg-m/sec (i.e. KI momentum required @ impact)
Therefore @
KI mass Effective Impact ΔV
1 MT 80 km/sec
5 MT 16 km/sec
10 MT 8 km/sec
[Clearly this is a substantial mission design challenge. Options to reduce these requirements include an earlier deflection, a higher assumption for β, an intercept angle close to 0 or 180 degrees (i.e. the angle between the resultant ΔV and the NEO velocity vector), a target miss distance closer to the Earth, etc. These would likely be offset however by consideration of the uncertainty in the NEO mass estimation, and other conservative assumptions given the early (if not the first) actual deflection mission]
Mission planning/Launch window considerations:
[This analysis requires detailed professional analysis. Thecursory analysis below is based primarily on a limited evaluation of launch window opportunities and consequent conditions at intercept with NEO 2011 AG5 by Dan Adamo, independent consultant. The primary results of his analysis are displayed in Fig 1]
Launch opportunities from 1 Jan 2023 (slightly prior to the assumed keyhole violation) through 9 Oct 2032 were evaluated with respective intercept epochs at the NEO of 31 Jan 2023 and 5 Aug 2033. An Earth parking orbit (EPO) height of 185 km was assumed. Hyperbolic excess velocities at Earth departure of less than 2.828 km/sec (i.e. C3 < 8.0 km2/sec2) are displayed in green, as are intercept velocities greater than 10 km/sec. Earth parking orbit trans-NEO insertion (TNI) ΔVs and Earth departure asymptote declinations are also shown.
Of particular note are arrival intercept angles and resultant effective relative velocity at impact. Since only that component of momentum transfer parallel to the NEO heliocentric velocity vector at impact produce the desired change in semi-major axis, these values are displayed for selected launch opportunities.
Of the opportunities listed, and assuming a deflection completion no later than 2030, the 12 Mar 2029 launch appears to provide the best result. With an arrival intercept velocity of 12.278 km/sec and an intercept angle of 130 degrees (the angle between the KI relative velocity vector at intercept and the NEO heliocentric velocity vector) the resultant effective impacting velocity is 7.967 km/sec retrograde. Given an effective total impulse requirement of 8e7 kg-m/sec to achieve the desired NEO deflection this would require a KI impact mass of just over 10 MT.
Inserting the parameters above into the online launch vehicle performance calculator provided by Silverbird Astronautics ( yields the following results for both the highest performing current LV (Delta IV Heavy) and the anticipated performance for the Falcon 9 Heavy. As can be seen the Delta IV Heavy falls short of meeting these requirements by just over 1 MT, whereas the projections for the Falcon 9 Heavy exceed the requirement by over 3.5 MT.
Delta IV Heavy w/long fairing
Launch Site: Cape Canaveral / KSC
Escape Trajectory: C3 = 6 km2/s2, 16 deg
Estimated Payload: 8905 kg
95% Confidence Interval: 7649 - 10259 kg
Falcon Heavy w/long fairing
Launch Site: Cape Canaveral / KSC
Escape Trajectory: C3 = 6 km2/s2, 16 deg
Estimated Payload: 13585 kg
95% Confidence Interval: 11060 - 16614 kg
Scenario 2. Keyhole Deflection analysis:
[Comment: Given the challenge apparent in the direct deflection (i.e. post-2023 encounter) analysis (above), consideration of the options for a keyhole deflection is warranted. This analysis, however, presents both a technical and a decision-making challenge given that such a deflection campaign would have to be initiated with a probability of impact (i.e. keyhole passage) considerably less than one. The following analysis assumes a keyhole passage in 2023 and makes the most favorable possible assumption for addressing this scenario; i.e. initiating the mission planning immediately and evaluating the potential for a successful keyhole deflection.]
Assumptions, definition of terms, comments: (in addition to those in the direct impact case above)
AG5 2023 keyhole characteristics:
Size ~ 100 km (ref. early estimate, Steve Chesley, Don Yeomans)
Deflection “leverage” ~ 50 (ref. early estimate, Yeomans, et al; JPL)
Keyhole encounter date = 3 Feb 2023
Earth impact date = 5 Feb 2040
Deflection effective ΔV required in 2023 for 1 Re displacement by 2040 impact (i.e. a 50 km displacement by 2023 keyhole encounter) ~ 0.5 mm/sec (approximation based on leverage of 50 and deflection completed by ~2019, i.e. 4 years between deflection and keyhole passage)
Net effective total impulse required (1 Re displacement) ~ 2e6 kg-m/sec
Net total impulse required (4 Re displacement) ~8e6 kg-m/sec
Momentum multiplier (β) = 2 (conservative assumption)
Net effective total impulse required for KI (assuming momentum multiplier acts parallel to relative velocity @ impact) ~ 4e6 kg-m/sec (i.e. effective KI momentum required @ impact)
[Note: This total impulse requirement is approximately an order of magnitude greater than the capability of a 1 MT gravity tractor towing a NEO for 1 year, even with “generous” performance assumptions. Therefore given the time criticality for a keyhole deflection the analysis below assumes the need, in this instance, for an observer S/Canda small kinetic impactor S/C combined deflection campaign.]
Therefore @
KI mass Effective Impact ΔV
1 MT 4 km/sec
0.5 MT 8 km/sec
This total impulse requirement appears to be within the capability of a kinetic impact mission. Nevertheless given that it would logically be preceded by a t-GT/observer mission, the first objective of which would be to precisely determine the need for a KI deflection, the sequential mission timing constraints indicate urgency in beginning this mission planning process. E.g. if one generously assumes a 5 year elapsed time from a decision to initiate an observer mission and its arrival at AG5 and determination of a precision orbit, this would leave only 2 years for completion of the KI deflection if the process were initiated now and completed by 2019 (as assumed above). If, as is clearly desirable, one were to await further tracking on AG5 prior to committing to a keyhole deflection (anticipated in September 2013) then two years would be removed from this (apparently) already tight timeline.
By this admittedly very rough estimate of the timeline required for an AG5 keyhole deflection, it appears that formal mission analysis and planning should begin soon, if not immediately.
3. Decision making challenge:
Given the conclusions above the decision process is confronted with the uncomfortable reality of considering a significant expenditure of resources juxtaposed with a low (but significant) probability of a 100 MT NEO impact. If a decision to initiate mission planning were to be made now its justification is a 1 in 625 probability of an AG5 impact in 2040. If a decision to initiate a keyhole deflection is deferred until after the next apparition of AG5 there would be a “penalty” of 2 years in the already challenging mission timeline in exchange for the “benefit” of minimal additional tracking (the 2013 apparition is beyond the capability of most of the follow-up observer capability) and, assuming a 2023 passage through the center of the keyhole, an increased impact probability of a factor of 2 -3.
While an impact probability of 1 in 200 provides somewhat greater rationale for committing to a keyhole deflection than the current 1 in 625, the delay in the time available to accomplish the mission is a severe penalty.
I emphasize again the approximate and rough nature of this analysis. Nevertheless the clear indication emerging from it is that, if even approximately correct, a professional, preliminary analysis of options is in order, and perhaps even urgent.
4. Geopolitical considerations:
The analysis recommended above is directly parallel to responsibilities recommended to the United Nations Committee on the Peaceful Uses of Outer Space (UN/COPUOS) by the Association of Space Explorers NEO Committee in its 2008 report to that body, Asteroid Threats: A Call for Global Response. ( In that report the ASE and its international Panel on Asteroid Threat Mitigation, recommended that, in order to address the required decision-making to prevent an asteroid impact, several functional responsibilities be needed to be established. One, an Information, Analysis, and Warning Network (IAWN) would handle the detailed information and analysis associated with assessing potential NEO impacts and ultimately, when appropriate, issue warnings to those who would be responsible for taking action in the public interest. A second functional responsibility, where pro-active mitigation (i.e. deflection) is indicated, is the Mission Planning and Operations Group (MPOG), in essence collectively those nations capable of mounting a deflection campaign.
Since 2009 the UN/COPUOS, and in particular its Action Team-14, who are leading the effort to establish a decision process within the UN/COPUOS, have been holding both IAWN and MPOG workshops in an effort to explore and implement a NEO impact threat decision process.
The analysis above is an example of the analytic work which the IAWN would perform, albeit in a professional and accurate manner. At such time that a potential NEO impact analysis indicates the need for mission analysis and planning (whether preliminary or final), the IAWN would communicate this to the MPOG and initiate appropriate interaction with them leading to a decision of whether or not mitigation initiation is appropriate.
The basis for international coordination in such a process is evident, not only in that NEOs will threaten impacts independent of national borders, but also in that any given impact threat, at the time a mitigation decision will have to be made, can only be specified as a probability of impact, which IF it hits at all, will do so somewhere along a line (generally) extending entirely across the Earth thereby passing through many nations. This is especially the case in the instance where a keyhole deflection is in play, i.e. where the impact probability is less than 1 at the latest date a decision to act can be made. This fact recommends that all nations along this “risk corridor”, each of which shares some probability of impact within its borders, participate in the decision process.
Furthermore a deflection process itself, while ultimately (assuming success) eliminating the risk for everyone, will temporarily, in the process of deflection, pose an elevated risk to certain nations along the risk corridor. For these reasons it is important that the risk corridor, and its implications, be understood by the international community in arriving at a collective agreement on how best to address an impact threat.
Given this realization it is also important in this case that an AG5 risk corridor be determined. Generally this is done by running a Monte Carlo simulation of the potential impacts of a set of “virtual impactors” reflecting the current measurement uncertainty in the knowledge of the NEO trajectory. Absent the capability to run a sophisticated Monte Carlo analysis I have nonetheless made a rough approximation of the AG5 risk corridor (Fig. 2). This is very approximate and should only be viewed as an example of the information which should be made available for planning and decision-making purposes.