Artemis needs Lunarship,
As I conclude this series
of Lunar Starship (LS) critiques, I respond to those who say,
"Criticizing is easy, but offering something perfect is much harder.
But before I present to you my vision for the Artemis Lunar Lander, I
want to briefly remind you of the main points of my critique of the
current Lunar Starship concept.
First, it should be clearly understood that the LS is unequivocally a
disposable vehicle. It has no wings, no thermoplate scales to return to
Earth, and it has no fuel to make even a launch from Moon satellite
orbit toward Earth (not to mention a braking maneuver near Earth by
Raptor engines to go into Earth satellite orbit). The lack of
reusability entails no need to maintain integrity during its mission.
In other words, LS can and should be multistage. Discarding unnecessary
junk on the way to the goal of the journey was invented by not at all
stupid people (Goddard, Zander, Tsiolkovsky), the fruits of their
wisdom are worthy of our attention and respect.
Secondly, the combination of two functions (the second stage of the
launcher and the spacecraft) in one vehicle burdens the LS during
maneuvers near the Moon with huge empty fuel tanks and too powerful
Raptor engines in the weak gravitational field of the Moon. Both fuel
tanks (for translunar injection) and six Raptor engines should be
separated immediately after the LS exit to the Moon, just as the
Saturn-5 rocket's third stage separated, which sent the Apollo missions
to the Moon. This Saturn-5/Apollo 3rd stage had a mass at LEO of 145
tons and was sending the Apollo spacecraft to the Moon with a mass of
45 tons and an empty 3rd stage with a mass of 15 tons. LS has a mass 10
times greater (1440 tons), which means it can send a FP of ~400 tons to
the Moon (taking into account the lower specific impulse of the
methane/oxygen fuel pair). This is more than enough to perform the task
of building a lunar base at the south pole of the Moon, not that to
deliver 2 astronauts to the surface of the Moon during the Artemis-3
Thirdly, the Raptor engines located on the lower end of the LS are
completely unsuitable for landing on the Moon (they can dig a hole,
where the LS will fall as a result) or for orbit takeoff (to dock with
the Orion spacecraft) in the absence of a launch pad with a gas exhaust
system, which no one on the Moon can build. Landing engines, like
takeoff engines, should be on top, like on the Dragon ships, then they
won't raise dust clouds interfering with visual control of the landing.
On the more recent LS renders, artists now draw a belt of engines
designed specifically for landing and takeoff. But two sets of engines
on one ship (LS) is something unprecedented in the history of space, in
modern slang - cringe. The Raptor engines were designed to fly in the
Earth's gravity field. Gravity on the Moon is 6 times weaker, so they
need completely different engines with an order of magnitude less
thrust than the Raptors. That's why the Raptor engines (along with the
giant empty fuel tanks) can and should be discarded on the way to the
Fourthly, the payload bay, raised to the height of a high-rise
building, not only raises doubts about the stability of the LS on an
unprepared lunar surface for landing, but also generates an absurd
elevator with open guides on the outer surface of the LS. Lunar dust
raised at the time of landing can settle on the elevator rails, which
makes their proper operation void of any guarantees. And a jammed
elevator (with tons of payload on board) makes it impossible to launch from
the surface of the Moon and dooms the entire mission to failure. In
short, the LS project has such a set of glaring shortcomings that its
unexpected victory in the HLS competition causes genuine amazement.
All of the above inspired me to propose an improved version of SpaceX's HLS, which I called Lunarship.
The Lunarship consists of
the lunar lander itself (above) and the upper stage for translunar
injection (below). The dry mass of the Lander (60 tons) and the dry
mass of the upper stage (80 tons) are obtained by dividing the dry mass
of the LS 120 tons with the addition of 20 tons for the baffles in the
ratio 3:4. On top Lunarship has 4 blocks of 2 methane engines, similar
to SuperDraco engines of Dragon ship. Each block has a thrust of 15
tons. The total thrust of all 8 engines (60 tons) is slightly less than
the total weight of the Lander in the lunar gravity field (~ 67 tons).
Consider the tasks a lunar lander must accomplish during its mission:
1) Braking near the Moon to enter Moon satellite orbit (ΔV= 0.82 km/s);
2) Docking with Orion to transfer the astronauts aboard the lander;
3) Landing on the surface of the Moon (ΔV= 1.73 km/s);
4) Stay on the Moon for the duration of the expedition;
5) Takeoff from the surface to the Moon satellite orbit (ΔV= 1.73 km/s);
6) Docking with the Orion spacecraft for the astronauts' return trip;
7) Disposal, or waiting for refueling and a new payload on the Moon satellite orbit.
Three of the seven tasks require significant fuel costs, consider them in reverse order:
5) Taking off from the surface of the Moon and achieving orbital velocity V = 1.73 km/s
V = I * ln(M/m) , where:
I is the specific impulse for the methane/oxygen pair of lander engines (3.68 km/sec);
M - starting mass of the lander on the lunar surface;
m - final mass of the lander on the orbit of the ISL, equal to its dry mass (60 t).
Solving the equation:
1.73 = 3.68* ln(M/60) , we find M = 96 t.
Thus, to take off from the lunar surface the Lander will need 36 tons of fuel.
3) Since the 3rd task of the lander is not only its landing on the
lunar surface, but also the delivery of the payload there, let's take
it into account by adding to 96 tons another 100 tons (payload).
Then m - final mass of the lander after landing should be 196 tons. Let
us find the initial mass of the Lander on the Moon satellite orbit before landing,
using the same Tsiolkovsky formula.
1.73 = 3.68* ln(M/196) The initial mass M at the beginning of the maneuver will be 314 tons.
Including 60 tons dry mass of the Lander + 100 tons of payload mass + 36 tons of fuel for takeoff + 118 tons of fuel for landing.
1) Deceleration near the Moon to enter Moon satellite orbit (ΔV= 0.82 km/s);
The first problem is to decelerate near the Moon to change the velocity
by 0.82 km/sec. Let's see how much fuel the Lander will need for this
0.82 = 3.68* ln(M/314) The initial mass of M at the beginning of the maneuver will be 392 tons.
Including 60 tons dry mass of the Lander + 100 tons of payload mass + 36
tons of fuel for takeoff + 118 tons of fuel for landing + 78 tons of
fuel for braking near the Moon. This value is only 8 tons less than the
assumed mass of the Lander (400 tons), obtained above by comparison
with the Apollo program. Thus, the above calculation confirms the
reality of creating a lunar lander with a total mass of 400 tons,
capable of delivering to the Moon the payload of 100 tons.
Now it remains to be seen whether the lower stage of the Lunarship can
give its upper stage the second space velocity during the maneuver
called translunar injection (ΔV= 3.22 km/s). The final mass
during this maneuver will be: 400 tons total mass of the lunar lander +
80 tons mass of the empty upper stage = 480 tons. According to
3.22 = 3.68*ln(M/480) The initial mass of M at the beginning of the maneuver will be 1152 tons.
Including 400 tons total mass of the lunar lander + 80 tons dry mass of
the upper stage + 672 tons of fuel for translunar injection. Thus,
compared to the LS (whose tanks held 1,200 tons of fuel) the Lunarship
can get by with much less fuel (904 tons), and thus fewer tankers for
its orbital refueling. This is the result of splitting the ship into
two stages, which is not difficult to see by comparing the two
calculations (Lunarship and LS).
Lunarship final parameters:
Starting mass of the complex - 1160 tons.
Lander's gross mass - 400 tons.
Dry mass of the lander - 60 t.
Total thrust of 8 lander's engines - 60 t.
Mass of the payload - 100 t.
Mass of lander's fuel - 240 t.
Total mass of the upper stage - 760 t.
Dry mass of the upper stage - 80 t.
Weight of fuel of upper stage - 680 t.
Total thrust of 6 engines of the upper stage - 1440 t.
History of my criticism of the LS:
http://cropman.ru/hls/ - Instead of Lunar Starship - Lunar Dragon!
http://cropman.ru/ls/ - Lunar Starship is conceptually wrong!
http://cropman.ru/ll/ - Seven Questions to Lunar Starship