Adam Hibberd
The Tunguska event holds a special place in humanity's collective memory as an incident which could have been so much more devastating had it not occurred in the heavily forested area of Siberia and instead in a more densely populated area . Yes trees were flattened yet it seems for this event at least, the fates were on our side.
However there has been a recent discovery of an asteroid with the potential of causing the same cataclysmic blast as Tunguska, and for which the loss of human life, though unlikely, nevertheless cannot be entirely ruled out. Note though that this would NOT be a global tragedy, only a local one.
The asteroid in question, 2024 YR4, currently rates as a 3 on the Torino impact hazard scale, a standard indicator of the threat to humanity (and Earth for that matter) of a celestial body, a quantity which depends on the likelihood of collision and also the energy of the consequent explosion were it to strike the Earth.
Cognizant of the extreme interest shown lately by NASA, and for that matter other national space agencies, in the field of planetary defence, exemplified in the recent impactor mission to the Didymos/Dimorphos binary asteroid system (DART), it seemed natural then for me to contemplate how a mission to 2024 YR4 may be realized, especially as I have developed software which would be ideal for precisely this sort of investigation (Optimum Interplanetary Trajectory Software - OITS). Furthermore I was asked to conduct this research by a US colleague of mine and I was pleased to undertake it.
So I set to work on investigating the feasibility of a mission to 2024 YR4 using OITS and found some remarkably interesting, as well as quite aesthetically pleasing results.
Take the first of the figures below, for example.
This is known in the field of mission design and astrodynamics as a 'Pork Chop' plot and expresses by colour, the feasibility of missions with a certain horizontal axis launch date (ranging in this case from 2025 to 2033) and a certain mission duration (vertical axis). The deeper blue the colour the more viable the mission, and also the yellower and brighter the colour the less viable the mission. Thus we see optimal launch windows (indicated by dark diagonal bands) arise firstly in late 2027 and throughout most of 2028, with a flight duration of less than 1 year; and secondly another window of the same shape from late 2031 to mid 2032.
It so happens that should the orbit of 2024 YR4 be constrained even further by future observations and found to intersect Earth's orbit at a time to actually collide with Earth, then this unhappy day for humanity would be around December 22nd 2032, so in other words it would be towards the end of the second diagonal blue-band on the above Pork Chop.
It seems if we are to send a mission to stake-out this PHA, then a launch in 2028, four years before the close encounter in question would be an extremely convenient means of doing so.
Look now on the plot below.
This shows a breakdown of the first of these aforementioned launch windows, from July 2027 to December 2028. We find that the evolution of launch C3 between these limits (red dashed line with right vertical axis) tells a very telling tale in that possible missions have virtually zero C3 (notice the right axis is logarithmic) from February 2028 to October 2028, a huge expanse of time, allowing for an extremely extended launch window of at least 8 months.
So all-in-all this analysis has revealed a wonderful window of opportunity exists for humanity to send a probe 4 years in advance of the danger year 2032, a serendipity which surely cannot be ignored?