Hot answers tagged

186

SpaceX uses an Actor-Judge system to provide triple redundancy to its rockets and spacecraft. The Falcon 9 has 3 dual core x86 processors running an instance of linux on each core. The flight software is written in C/C++ and runs in the x86 environment. For each calculation/decision, the "flight string" compares the results from both cores. If there is a ...


111

In this AMA by the SpaceX software development team, they wrote: We've been getting a lot of questions about how C#/MVC/etc have to do with rockets. They don't. About their development they said: The Flight Software team is about 35 people. We write all the code for Falcon 9, Grasshopper, and Dragon applications; and do the core platform work, also on ...


97

There's actually a few outcomes of the second stage that can occur (and some interesting tales to go along with them), but as geoffc has mentioned, second stage reuse is no longer planned for Falcon as Musk thinks the resources to develop it are better spent elsewhere. It's not an insurmountable technical challenge. Intentional Deorbit This is done for ...


93

Ironically, the answer is in his own (or rather SpaceX's) video. Still from 0:49 of the video showing cold gas thruster firing The first stage of the Falcon 9 uses a set of nitrogen cold gas thrusters to perform its flip after separation, and you can see them repeatedly firing in the video. As the compressed gas leaves the thruster its pressure drops very ...


93

'Starman' is a mannequin (store dummy) wearing a real SpaceX developed space suit that was a qualification unit, used in designing the space suit for the Commercial Crew program. During the SpaceX Grasshopper program, where they tested landing a first stage in McGregor Texas they mounted a dummy with a cowboy hat on the base of the Grasshopper vehicle. ...


92

Making a car run when it's been stored on Earth for 10 years can be a challenge. Storing it in space makes things worse. All lubricants will have evaporated. Cold welding is a possibility. The thermal environment is a variable. If the car + payload adapter tumble, the car will spend time in the shadow of the adapter, and you get thermal cycling which will ...


90

You see that tiny thing on the far left? That's the Falcon 1. It's a comparable size to Blue Origin's New Shepard spacecraft and SpaceX's Grasshopper (which accomplished a similar feat 6 times, around 3 years ago, but didn't *technically* enter space). You see those 3 in the middle? That's what SpaceX landed today. Grasshopper / Blue Origin were ...


90

No, because it is not in Earth orbit First the payload does have a purpose: it is a boilerplate, and those have a purpose, namely to "test various configurations and basic size, load, and handling characteristics of rocket launch vehicles". Second, you are asking... is the car equipped with a propulsion system to change its trajectory in case of ...


90

I can't speak for why SpaceX made the decision. However, while three legs won't wobble, four legs are less likely to tip over. SpaceX has demonstrated tipping over is a major problem. Dr Peterson of The Math Forum explains... There are different kinds of stability! A three-legged stool is guaranteed not to wobble, because the ends of its legs always ...


81

Methane has the benefit of being easier to store than hydrogen. Mostly passive cooling can suffice to keep it cryogenic, whereas hydrogen needs active cooling, and will still vent over time. Which makes Methane much closer to 'storable' than hydrogen can be. This would make it useful for deep space missions, with long mission durations. Methane is less ...


76

They are used to redirect lightning in the immediate area. This essentially creates a faraday cage, shielding the rocket from being fried by lightning. You can see how high the towers reach, high enough to ensure there is no risk of lightning hitting the craft. Update by @highonrope: The rectangle which the rocket launches through is huge...from the ground ...


69

The Falcon 9 can shut off a faulty engine, re-configure the remaining engines (change thrust levels, vector direction) and update its flight profile in real-time. This happened on the SpaceX CRS-1 flight (see also this article). The Merlin engines can be gimbaled (change the direction of thrust), so on the Falcon 9 all engines can slightly change the thrust ...


68

It seems to me that the SpaceX Starship rockets have sort of a homemade quality to them, like they were made in someone's garage with basic tools That is because they are! The "zeroth" prototype, Starhopper was built from November 2018 to March 2019 literally in a dirt field in Texas, in the open air. When Elon Musk announced in December 2018 that ...


65

The boosters do not have the range to get to Africa because they aren't going fast enough. If you look at the graphic below it shows a Falcon Heavy mission. The side boosters do not get very far downrange at all so they return to the cape. The drone ship for the core booster was located 1236km downrange, Africa is over 6000km downrange. The graphic came ...


64

In two words: Precision landings. Underlying all of SpaceX's decisions is the desire to go to other planets, especially Mars. For exploring the solar system, Elon Musk feels that precision landings are extremely important. The precision landing requirement means that you want to start slowing the spacecraft before you reach the surface, which points ...


63

There are many key points to this, probably none on their own sufficient to ditch the parachutes approach (except economics, those are good enough on their own), but together they make for a compelling case against it; Descent control: As already mentioned, there's a significant guidance uncertainty with the use of a parachute system. Some of it comes from ...


63

Yes, it's space junk: after about 6 hours, the second stage will stop working and there will be no way to change the trajectory of stage and payload. So it's a non-functional satellite, i.e. junk. An object whose course cannot be controlled, and a potential future navigation hazard. It's not in Earth orbit, so it's unlikely to cause a problem here. There is ...


61

The purpose of Starship is not merely to put satellites into orbit for cheap. If that were its purpose then you'd be correct; it's way overbuilt for that. Starship wasn't created to put satellites into orbit though, it was created to construct a self-sustaining city on Mars. Achieving that goal will likely require lifting hundreds of megatons of mass to ...


59

According to Elon Musk's Twitter it's in the glove compartment, alongside a copy of Hitchhikers Guide to the Galaxy, and the Foundation series on the Arch disk.


59

The fairings are not boats. While they appear to float (at least for some time), there will also be water on the inside of the fairing. That results in some issues. Inside the fairing, there are electronics and other corrodable materials. Now the fairing is designed to be as light as possible. Therefore, SpaceX probably doesn't want to make the entire ...


58

My (somewhat educated) speculation: deposited contaminants due to outgassing from the various polymers on the dashboard and/or the hood. Vacuum and UV exposure tend to break down nearly every polymeric material. The volatile compounds that fly off in the process would deposit themselves as a haze on the windshield. As a side note, this is one reason you ...


57

The heat of re-entry is highly dependent on speed. The second stage of the rocket is responsible for providing most of the speed needed for orbit, after the first stage lifts it out of dense atmosphere. Falcon 9 separates its first and second stages at relatively low speed, so its reentry starts off drastically slower than a reentry from orbit -- about ...


57

Red Dragon was intended to piggyback on the effort to develop and qualify Dragon for propulsive landings on Earth. The qualification hit a snag: NASA requirements for human-rating the propulsive landing system were so stringent that SpaceX decided they didn't want to spend the time and money to meet those requirements. That left development of the landing ...


57

First of all, a typical launch window for going towards Mars is about 2.5 hours maximum. As a goal is to send the payload towards Mars, that is one limit to the window. Also, there are a number of other factors affecting a launch. These include: Availability of the range Personnel that are required. A lot of people are required on launch day from quite ...


57

One of the keys to SpaceX's cost advantage is standardization on common parts. One example is the Merlin engine, which is used on both the first and second stages of the Falcon 9 and Falcon Heavy (though a slightly different vacum optimized version on the second stages). This is also done for fairings. Fairings are very expensive to make (around $6M). ...


57

There are many reasons. They include money, intellectual property, regulations, and Elon Musk. Money. Building open source software is relatively inexpensive, sometimes ridiculously inexpensive. No equipment is needed as most programmers have their own computers. There are many open source software projects where the developers do their work for free. ...


57

By design that will never happen. There are always enough return seats for the crew. This is exactly why the whole crew of one of the visiting vehicles gets in it whenever it undocks, even when it is only being moved from one docking port of the station to another the crews retreat to their vehicles in fire / leak / toxic atmosphere emergencies the crews ...


56

It is still way too early to make such a judgement. It's easy to be overly optimistic about the cost of a program. The Space Shuttle was supposed to have dozens of flights each year and be super-cheap because it was reusable. However, you simply don't know the true cost until a program has been in use for several years. After several years of the Shuttle, ...


55

He most certainly is. The seatbelt can be seen clearly across both his shoulders. It is currently unclear whether or not the miniature Starman sat on the dashboard has a seatbelt. Apparently he is also sewn into the seat. Source is Quora, so meh, but interesting.


53

The display shown is from the screen of one of the Space Station Computer laptops in the US Lab. This was being downlinked to Mission Control in Houston to monitor the functioning of tools used by the ISS crew to track the Crew Dragon's approach. The foreground program is the Dragon 2 Docking Monitor, which takes video supplied by the Crew Dragon (aka ...


Only top voted, non community-wiki answers of a minimum length are eligible