Adam Hibberd
Ariane 6 is the up-and-coming successor to the old Arianespace workhorse, Ariane 5, and may secure its maiden flight later this year. There will ultimately be two strap-on booster configurations from which to choose, one with two boosters, and the more powerful version with four.
I thought it might be worthwhile assessing the viability of the latter more powerful variant for the intiative known as Project Lyra, which is the feasibility of missions to the first interstellar object to be discovered, 1I/'Oumuamua. To this end I looked at some performance data available for it both on Wiki and in its User Guide, a version of which is available online here.
Referring to the latter document, it becomes quite clear that Ariane 6 4 would simply NOT be powerful enough to reach Jupiter directly with any useful payload, and frequent visitors to this blog will know how important a Jupiter encounter is in order to achieve any kind of realistic mission to 'Oumuamua with chemical propulsion.
Given this fact, does that totally discount a mission with Ariane 6 4?
The answer is no for one very clear reason: the V-infinity Leveraging Manoeuvre (VILM).
A VILM is a useful mechanism by which the speed of the s/c relative to the Sun can be augmented via exploiting the Earth’s mass with a gravitational assist (GA) of the planet. Furthermore the C3 is significantly reduced by this device.
From the User Guide, we find that a Lunar Mission, which has a characterstic energy C3 of just about 0.0 km2s-2, can achieve a mass of around 8,600kg, whereas the corresponding C3 to Jupiter would require around 84 km2s-2 , so the former is a much less challenging prospect for the Ariane 6 4 launcher.
For a VILM, the spacecraft (s/c) embarks on an Earth-return heliocentric elliptical arc, with a time-period of n multiples of Earth’s year (365 days), where n is a whole number, usually 1, 2 or 3.
You may like to verify yourself that the hyperbolic excess relative to the Earth, V∞ (the speed with which the s/c escapes Earth's gravitational sphere of influence) required for the n=1 option (i.e. in 1:1 resonance with Earth) is precisely zero and since C3 = V∞2, that means C3 is also zero, as is required.
So we have 8,600kg of capacity for Ariane 6 4, if we introduce two further boosters ‘into the equation’, refer Table 1, then that gives us a total of 6,727kg, well within the scope of an Ariane 6 4. Let us further assume a s/c payload mass of 100kg, yielding a total of 6,827kg (there is still capacity for more, but this shall do for the moment).
| Booster Stage | Exhaust Velocity (kms-1) | Total Mass (kg) | Dry Mass (kg) | Propellant Mass (kg) |
| STAR 63F | 2.9106 | 4590 | 326 | 4264 |
| STAR 48B | 2.8028 | 2137 | 124 | 2013 |
Applying Tsiolkovsky using these two stages, we get a total ΔV generated by this pair of boosters as 9.30kms-1. Take it as read, that it is best to apply ALL this ΔV at the Earth return, and NONE at Jupiter itself, thence utilising a passive GA at Jupiter to eventually arrive at the target, ‘Oumuamua. (To reinforce this, note that the STAR 63F would only be able to deliver 2.85kms-1 of ΔV to a STAR48B +100kg payload, which would be quite insufficient to reach Jupiter – thus both stages would need to be fired at Earth return.)
It is now time to run my personal software development Optimum Interplanetary Trajectory Software (OITS) in order to determine whether these parameters, combined with the E-DSM-E-J-1I series of encounters, would result in viable missions to the interstellar object in question.
The outcome is that there are two candidate years for launch with an Ariane 6 4, 2030 & 2031. For the 2030 launch we have arrival at 'Oumuamua after 56 years, whilst with the alternative launch option in 2031, this has a flight duration well over 100 years.
All this effectively rules out the Ariane 6 4 launch vehicle for missions to ‘Oumuamua, unless some alternative, hugely more effective propulsion system can be harnessed in place of the solid propellant stages adopted here.
