Elon Musk has stated that he will consider it a success if the Falcon Heavy gets far enough away from the launch pad to not cause damage if it blows up. The Falcon Heavy underwent a 12 second static fire. Let's say there was some critical issue that wouldn't show up until just after the duration of that firing. Would the Falcon Heavy be far enough to not cause significant damage to the launch pad in 12 seconds?
$\begingroup$ What did the most damage during the Amos-6 event? The explosion itself? Fuel spilled onto the pad and burning slowly? If the latter then just spilling the fuel from some height might help mitigate the problem by mixing it with air and burning fast still in the air? $\endgroup$– jkavalikFeb 5, 2018 at 16:12
2$\begingroup$ Well, after 12 seconds, it will be about 450 meters up (source: math), but I don't know how much damage would be caused if it failed from that distance. $\endgroup$– internet_userFeb 5, 2018 at 16:47
$\begingroup$ It depends on when they start their pitchover maneuver. If it's still going straight up at 12 seconds and 450 m altitude (which works out to an average acceleration of 6.25 m/s^2, which sounds a bit high for the liftoff phase), damage to the pad & its structures from the failure: minor. Damage from the impact of some 8,000 MT falling from >450 m, & the resulting conflagration: major. At 6.25 m/s^2, 12 s yields 75 m/s upwards, so continue upward ~7.6 s, ~287 m, then ~13 s to the ground (missing the stand). If pitchover occurs before ~10 s, even 1 m/s of lateral velocity misses the structures. $\endgroup$– Tom SpilkerAug 18, 2021 at 17:07
$\begingroup$ Of course, the above assumes that the malfunction doesn't steer the stack toward the structures! $\endgroup$– Tom SpilkerAug 18, 2021 at 17:08
Not even close. In fact, at 12 seconds in, you're looking at maximum damage to not just the pad itself, but the surrounding area as well. You're going to have tons of debris (most of it burning and possibly carrying even more unburnt fuel) fall from 1500-2000ft range in a giant umbrella of destruction.
In 1997, a Delta II carrying the GPS IIR-1 satellite exploded 13 seconds in. While nobody was killed, check out the video of what happened to the vehicles parked outside the blockhouse.
18$\begingroup$ It’s possibly worth noting that Falcon Heavy is approximately ten times the size of the Delta II producing that rather impressive explosion. $\endgroup$ Feb 6, 2018 at 2:01
1$\begingroup$ In the comments, internet_user estimates that it'll be about 450 meters up, which is actually a bit high for optimal damage from an 8kt explosion. $\endgroup$– MarkFeb 6, 2018 at 9:43
5$\begingroup$ Umbrella of Destruction - thanks for naming my new metal band. Or DND spell. Maybe both. $\endgroup$– corsiKaFeb 6, 2018 at 15:33
$\begingroup$ The Delta II had SRBs which are much worse than liquid fuel detonations. $\endgroup$– JoshuaFeb 7, 2018 at 22:04
$\begingroup$ OTOH Delta was fueled by RP1, with SRBs strapped on, meaning pretty much a napalm bomb when exploding. Liquid methane evaporates very rapidly if set on fire, so it's quite probable nearly nothing would be on fire by the time of reaching the ground. $\endgroup$– SF.Aug 19, 2021 at 14:06
To avoid damage to the pad, the rocket must have traveled down range far enough that if it exploded, the debris would not land back on the pad. The issue isn't height, it's horizontal distance. 12 seconds, as mentioned above, wouldn't get you downrange much. 30 seconds definitely would.
According to the Falcon Heavy press kit, the engines are lit about 5 seconds before launch. The acceleration should be a bit faster then a standard Falcon 9 mission. Let's look at the last launch seen below:
In the above image, at T+0:09, the rocket still appears to not have cleared the tower. I'm sure the Falcon heavy will accelerate quicker, but even at T+0:12, it still is only a few hundred meters above the ground. It takes until T+0:25 until it is a full kilometer away.
A few other points of reference. Max Q happens at about 1:06 for Falcon Heavy, 1:10 for Falcon 9. It seems that the acceleration won't be significantly higher during the early stage of flight. The biggest gain seems to come from using the middle core less until outside of the atmosphere.
Bottom line, if anything that results in an explosion within the first 30 seconds after engine ignition happens (T+25), I strongly suspect there will be significant damage to the launch pad. And if it happens within T+15s of launch there will almost certainly be at least as major of an effort to fix as with the previous explosion.
When I was reading LM-3A series LV User's Manual I found this information:
In the period between T0 and T0+15 sec (for LM-3B), or T0 and T0+17 sec (for LM-3A/3BE/3C), the LV will not be destroyed by ground command even though an anomaly occurs, unless LV explodes itself. This is to ensure that the launch vehicle flies over 400 m (range protection radius) away from the launch pad for the protection of the launch facilities.
LM-3B weighs 425t, less than 1/3 of a Falcon Heavy, so it's safe to assume that Falcon Heavy needs more than 400m of down range clearance and more than 15 seconds to get there.
I have not found this information in the Falcon User's Guide.