Podcast #128: We chat with Kent C Dodds about why he loves React and discuss what life was like in the dark days before Git. Listen now.
100

During the Pathfinder landing the airbag system hit the ground at about 20m/s. This seems fast but compared to other space speeds, it's very slow. When the pathfinder rover arrived to land at Mars, it was cruising at around 7300m/s. To get this velocity to zero, the parachutes, heat-shield, and single-fire rocket engine did their work to kill the velocity ...


84

Does the US have some secret insight into landing on the moon? Yes: fail early and often. The US developed experience with uncrewed landings first, before attempting crewed landings in the Apollo program; those earlier programs had a very high failure rate. The first US lunar spacecraft were in the Ranger program, which was simply attempting to hit the ...


78

The USSR flew three successful automated lunar sample return missions: Luna 16, Luna 20 and Luna 24. The probes landed on the Moon, collected samples, and started a small rocket with the samples back to Earth. The returned mass was very small (101 g, 30 g and 170 g, respectively).


76

All the lunar landings were performed with the sun low in the sky behind the LM, between 5º and 14º above the horizon at the landing site. This provided several advantages: The sun wouldn't be in the crew’s eyes during any portion of the descent (they’d start out oriented feet forward, lying on their backs looking upward, during the braking phase, and ...


71

No. Planting a flag was the idea of NASA's "Mr. Fix-It", Jack Kinzler, less than 4 months before Apollo 11's launch: Kinzler believed that the people of the United States would also want to see an American flag to commemorate the enormous achievement of landing a man on the surface of the moon. The original LM design had an American flag painted on the ...


53

Two main reasons really: The dust on the Moon, while it would be extremely fine-grain, is also highly charged due to Sun's radiation and solar winds, so it would stick quite good to the surface, grain to grain, but also cling to astronauts' space suits, something that was made quite apparent when they had fairly big problems getting it off and somewhat ...


52

Chandrayaan-1 hit the Moon at high speed and did not survive its "landing", which would have been much more difficult to engineer. (Its successor, Chandrayaan-2, which will actually land, is expected to cost \$125 million and has taken more than ten years so far, as opposed to the three years for Chandrayaan-1.) As far as cost goes, besides India's own (...


48

EVA suits are very difficult for a single person to put on by themselves, so another person was required to help the other astronaut put on their EVA suit. At the very least, it is much easier to do it with help. A single person would have a very difficult time doing this. On the ground a team of people is usually employed to have this happen. Note there are ...


47

Grumman hadn't reached the weight targets for the LM at the time of Apollo 10. Snoopy weighed 197 pounds (89 kg) more than Eagle, according to Apollo By The Numbers. However, this would not have made safe landing impossible. Apollo 11's LM carried a 300-pound descent fuel margin above and beyond all the specific contingencies that were accounted for (stuck ...


44

The Moon is much harder to reach. I'd suggest the biggest reason for more visits is popularity and politics. The Space Race was about tactical advantage (and to a huge extent posturing) between the Soviet Union and the United States. Both countries wanted to show the other just how big of an ICBM each could make. Deepsea diving does not provide the same ...


43

It's a cute story, an urban legend, but that's all it is. According to NASA HQ Apollo 11 Lunar Surface Journal that includes full transcript and MP3 audio clip (52 MB) of all the conversations between Apollo 11 astronauts and mission control, as a note near the beginning of the page, there it stands: During November 1995, a clever (and slightly risqué) ...


41

These were the "1202" and "1201" program alarms, which were warning signals that the lunar module's computer was becoming overloaded. During Apollo 11's descent to the moon, the crew left the LM's rendezvous radar, which was used to find their way back to the command module, switched on in the "SLEW" mode, so it would be ready if they had to abort the ...


40

After these 25 second would have ended, the LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why using two stages which surely ...


40

Some pictures from Apollo 11 of the landing gear – struts, footpads and contact probes. Three Apollo 12 images: Two Apollo 14 footpad images: An Apollo 16 image: The two probes bend straight up on the left of the left and right footpad. I found no Apollo 17 images with visible contact probes. So yes, some contact probes did bend and stick out sideways. ...


39

Actually there’s no reason that an airbag system could not be used on the Moon, nor that it could not be a good design decision in some circumstances. The MPF and MER airbags took out the last 10 to 26 m/s of velocity. The reason that there was that much velocity left was the accuracy, or inaccuracy of the solid rocket motors’ total impulse, along with ...


37

They used the Lunar Landing Training Vehicle, as pictured below. This had a jet engine to provide 5/6 of the lift needed to hover the vehicle, plus rocket engines that simulated the LM's engines. With the jet running, the LLTV felt like it weighed 1/6 of its actual weight, so it came pretty close to simulating moon gravity.


36

Great question. The exhaust velocity from typical landing engines is about 3 km/s. You can imagine good-sized particles being accelerated to a significant fraction of that, say 1 km/s, which is the muzzle velocity of a rifle. There is nothing in the vacuum to slow them down, other than eventually hitting something, or the ground. 1 km/s is already a good ...


35

Even before Kennedy's "we choose to go to the Moon" speech, NASA was working on concepts for Moon missions. Dr. Robert Gilruth, Director of the Manned Spacecraft Center: "Even before the President's decision to land on the moon, we had been working on designs and guidelines for a manned circumlunar mission. This was done in a series of bull sessions on ...


35

It is correct that the probe on the forward footpad was omitted to avoid interfering with the ladder: The probe located on the forward landing gear was deleted because of a concern that the failed probe could interfere with crewmen descending the LM ladder. [p. 8] There was more than one probe for redundancy. In particular, there was no electrical ...


35

While engineering and available technologies have greatly advanced since the 50's and 60's, safely landing something on the moon is still a highly technical feat with a critically long list of potential failure points. After a quick look at a list of moon missions, it appears that the US alone has had more launch failures than India and Israel's combined ...


33

The Lunar Roving Vehicle did have a (form of) compass. It was gyroscopic rather than magnetic, thus it needed calibration when first powered up using the sun angle as a reference. It's in the upper left of the console here: According to Wikipedia: Navigation was based on continuously recording direction and distance through use of a directional gyro and ...


30

Most of the Apollo photo libraries have a few shots of the surface under the descent engine bell; I think A14 has some interesting ones: The disturbance of the soil is very subtle; compared with the surface further out, I see more 1-2cm-sized pebbles, suggesting that smaller particles have been blown away from under the engine. The lack of a massive blast ...


29

The simplest would be defining some arbitrary impact velocity that is at the limit of being fatal, and we then consider everything else (surface properties, subject's physique,...) except gravitational acceleration constant. We can also neglect air resistance to make it simpler, since we're more interested in a safe height to jump off on the Moon, than that ...


29

Some switches were normally left in one position for the entire mission, and would only be changed in unusual situations. One particular semi-famous example is the switch controlling the power supply for a module called the Signal Conditioning Equipment (SCE), which was necessary for sending telemetry from the spacecraft to mission control. It had two ...


28

Yes. There is a lot of good information in this presentation from the June 1966 Apollo Lunar Landing Mission Symposium relative to landing flight design including abort planning. The crucial figure is this one: which shows the capability of the ascent engine to abort all the way down to landing. It assumes a 4 second delay to separate the landing stage. ...


28

I purchased "The Apollo Guidance Computer: Architecture and Operation" to answer this question (an excellent read). And the answer is yes it might be possible to land on the moon unmanned. However, a number of checklist items would need to be skipped, mostly numerous inertial system checkouts/alignments, most importantly for the gyros. They need to be within ...


28

The Apollo LM had three independent propellant supplies: tankage in the descent stage usable by the descent engine, tankage in the ascent stage for the ascent engine, and in the ascent stage for the reaction control system (RCS) thrusters. Prior to the initiation of descent and landing, only the RCS would be used, and very little of it. During the ...


25

In this video of the Apollo 11 landing, you can see dust being blown away during the approach (from ca. 4:30). Some of the particles were blasted clear over the horizon and may have ended up halfway across the moon. The 'ground' below the dust isn't smooth. Like new basalt, it has a grainy texture, as you can see here directly below the exhaust: The ...


25

Apollo 11 (AS-506) was considered to be the first landing mission. And yes, up to early 1969 nobody thought the plan out thoroughly enough. Note on lunar module crew positions: Neil A. Armstrong - commander Edwin E. Aldrin, Jr. - lunar module pilot Above them, in the 183x186 orbit: Michael Collins - command module pilot Now let's see: Chariots for ...


25

Three legs offers less safety margin for steep slopes and sideways landings. If a three-legged lander touches down on a steep slope such that the center of gravity of the ship is outside the triangle formed by the contact points, it will tip over. The four-legged lander has a substantially larger area inside the quadrangle formed by the contact points; as ...


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