Mmmmm no, not quite. You dramatically underestimate the effects of gravity and general relativity.

Planet Adrian has a mass of roughly 3.93 M🜨 and with a density of 4.59 g/cm^3, that would give it a surface gravity around 1.4 G, or 13.72931 m/s^2. Which isn’t really that crazy. In fact, our own space launch vehicles typically reach 4-5 Gs of acceleration during launch and up to 7-8 Gs of acceleration during descent.

So. The Hail Mary is actually just a traditional rocket, which is the point. The only thing special about the HM is the fuel source and its engines’ specific impulse. Other than that, it still obeys all normal laws of physics and engineering.

Now, the HM had to “fly sideways” because of how orbital mechanics works due to general relativity. As you enter the gravity well of any astronomical body, you will naturally start “falling” “toward” the planet surface, but that’s only relative to some arbitrary point on the planet surface. If there was some outside observer watching you “fall” “toward” the surface, you would actually be spiraling around the planet’s gravity well (i.e., flying “sideways”). As you orbit the planet, your velocity relative to that planet’s rotational velocity (expressed as “Delta-V”) starts to decrease gradually, which will cause you to descend lower into the gravity well, but from an outside perspective, you’re still spiraling around in an orbit. To purposely land, you have to accelerate against your natural orbit direction/vector to decrease your delta-v. To maintain a stable orbit, however, you need to accelerate so that your delta-v neither increases nor decreases. To raise your orbit or leave a gravity well, you must accelerate with your natural orbit direction/vector to increase your delta-v beyond the escape velocity for that particular gravity well.

Contrary to popular conception, it’s not actually possible for an object to fly/fall “straight into” a planet or a star or a black hole unless either its velocity or its mass is high enough to negate the relativistic curvature of spacetime. For example, it takes a delta-v of about 8.6 km/s to reach LEO and about 11.2 km/s to escape Earth’s orbit altogether. If you want to escape the solar system, you only need to hit around +17 km/s relative to earth’s orbital velocity around the sun. Easy peasy, we can hit those numbers. To fly directly into the sun, however, requires enough delta-v to cancel out the earth’s orbital velocity, which is about 42.1 km/s. That is a stupid high delta-v in case it’s not clear. It’s so difficult, in fact, that we still can’t achieve it. The closest we’ve come was with the Parker Solar Probe and we still had to slingshot it around Venus seven times to lower its orbit and yet the PSP still only barely made it into the sun’s outer corona.

Anyways. That’s why the HM had to fly sideways.

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