Robert Goddard, a Massachusetts-born physicist, launched the world’s first liquid-fueled rocket on this date 100 years ago.

It was not an overly impressive flight. The rocket, fueled by gasoline and liquid oxygen, rose just 41 feet into the air, and the flight lasted 2.5 seconds before it struck ice and snow.

Nevertheless, this rocket, named “Nell,” represented a historic achievement that would help launch the modern age of spaceflight. Three decades later, the first objects would begin to ride liquid-fueled rockets into space, followed shortly by humans. A little more than 40 years would pass before humans walked on the Moon.

To mark this historic moment, a few Ars staffers are sharing some of their most memorable launches. Please add yours in the comments below.

This page lists various fan-made tools that can help calculations related to the gameplay of Kerbal Space Program. Unlike addons, they do not directly influence the game, as they are run separately.

Performing a transfer from an orbit of one body directly to an orbit of another one seems like serious business. A few guides published on the forums have a lot of maths and stuff, you may think this is too complicated to figure out.

Well, it is rocket science, but: it's not complicated.

In the basic orbiting tutorial, you were introduced to the concept of orbiting, and basic orbit stabilization, as well as an orbital table to help you along. Now, what if you want an orbit that isn't on that table? What if you want to have an orbit with a specific period? That's where these formulae come in.

In the basic orbiting tutorial, you were introduced to the concept of orbiting, and basic orbit stabilization, as well as an orbital table to help you along. Now, what if you want an orbit that isn't on that table? What if you want to have an orbit with a specific period? That's where these formulae come in.

The blue circle is Kerbin itself, the light blue circle around it is the top of the atmosphere. You can click+drag on the left of Kerbin to set periapsis, or on the right of Kerbin for apoapsis. You can also use the text boxes to enter altitudes and velocities numerically.

You need to specify two values in all: either altitudes of periapsis and apoapsis, velocities at periapsis and apoapsis, or both altitude and velocity at either periapsis or apoapsis. You select the values you want to enter with the Parameters menu, the remainder of the information will be computed from the values you put in. If you enter altitude and a velocity above escape velocity, it'll give you excess velocity at infinity. The apoapsis and periapsis textboxes are altitudes above mean sea level (AMSL), the text report below has both altitudes AMSL and distances from the center of Kerbin. Note that if you specify values that lead to an apoapsis lower than periapsis, the plotted orbit and contents of the text fields will be swapped automatically.

This online tool calculates delta-v and CommNet requirements in KSP (a video game, Kerbal Space Program). It helps KSP players plan and solve complex missions. Just like the game, these calculators are made to be interactive and visual to help new players quickly grasp the mechanics of rocket science.

How to Use: Simply select the body you wish to perform orbital synchronization calculations on from the drop-down list, then pick the resonance you wish to place your craft in. Example: If you wanted a 2:3 resonance, enter 2 into Numerator and 3 into Denominator.

On September 26, 2022, NASA’s Double Asteroid Redirection Test (DART) spacecraft crashed into a binary asteroid system. By intentionally ramming a probe into the 160-meter-wide moonlet named Dimorphos, the smaller of the two asteroids, humanity demonstrated that the kinetic impact method of planetary defense actually works. The immediate result was that Dimorphos’ orbital period around Didymos, its larger parent body, was slashed by 33 minutes.

Of course, altering a moonlet’s local orbit doesn’t seem like enough to safeguard Earth from civilization-ending impacts. But now, as long-term observational data has come in, it seems we accomplished more than that. DART actually changed the trajectory of the entire Didymos binary system, altering its orbit around the Sun. //

Because Dimorphos orbits Didymos, some of the ejecta remained trapped in the system, where it altered the mutual orbit between the two rocks. But a crucial fraction of the ejecta achieved escape velocity from the entire binary system. The momentum carried away by the system-escaping debris is what ultimately contributed to shoving the center of mass of the whole Didymos-Dimorphos pair. “In our case, we found that the beta parameter due to DART impact was around two,” Makadia explained.

The debris blasted completely out of the Didymos system gave the asteroids a push roughly equal to the initial impact of the spacecraft itself. //

The goal of DART was primarily to take our planetary defense out of the realm of computer models and get us some hands-on, practical experience, and Makadia thinks we succeeded in doing that. “Our work proves that hitting the secondary asteroid is a viable path for deflecting a binary system away as long as the push is large enough,” he said. “This wasn’t the goal of DART, but we can always design a bigger spacecraft.”

Statistical Ars Legatus Legionis
15y
54,490
michaeltherobot said:
You clearly know what you are talking about, so could you ELI5 why polar LLO costs more than equatorial LLO? My intuition that they are the same comes from KSP, in which, soon after leaving Earth orbit, you plan a miniscule burn to adjust lunar insertion from coming around the side to coming over the top.

Of course, in both those cases I then have to decelerate hard at perilune to be captured. Perhaps the flight paths NASA is considering have some way to save dV vs my hard deceleration, which don't work for polar orbits?

The added cost comes from the plane change and plane change at high velocity (low orbit) are expensive. You CAN do something similar to what you describe it just takes longer potentially much longer. The higher the perilune the cheaper the plane change becomes but the longer it takes to reach the perilune. You drop yourself into a highly elliptical orbit around the moon at the same plane as the initial orbit. You then ride up to the perlune, raise the plane to 90 degrees and lower the perilune to circular (decelerate hard).

NASA wouldn't consider doing a plane change in Earth orbit because then you can have a free return trajectory which is a risk reduction factor.

So the tradeoff of DeltaV vs time.

Compare this map to the one in the previous post.

https://arstechnica.com/civis/attachments/1772816223709-png.129833/
1772816223709.png

Significant cheaper but it adds a 3.5 day loiter riding up to the vey high perilune to become as cheap as NRHO (including the transit). To have insertion and exit cost that are 2x this you would need the same loiter on the way back. In KSP things like mission duration are quite cheap and excessive risk doesn't matter but yeah same basic concept and math.

To be clear this is really only an issue for an occupied crew vehicle. If you add a 15 day loiter then the phase change becomes essentially free. For prestaging the lander or the tanker to refuel it after a sortie neither would be harmed by a 30 day longer mission. So if LLO was used as a staging point, which I don't think it will, then there would be mission choices by SpaceX and BO on how much LLO loiter vs round trip DeltaV for sending that tanker to meet lander with the prop it needs.

Statistical Ars Legatus Legionis
15y
54,490
Polar LLO is really hard to get into. Even with a less dumpy crew vehicle bringing it all the way day to Polar LLO and back is dubious. I know know it runs against the popular trend of everything NASA does is stupid but the math doesn't lie.

I got this some years ago when NASA removed the sensitive restriction. Not sure it is available anymore. NASA is pretty bad about maintaining public access to old reports. It was created in the analysis requirements for Constellation.

A direct LLO requires a huge amount of DeltaV to enter and leave when talking about polar landing sites. This is because you need to do an up to 85 degree plane change Exactly how much depends on where exactly you are landing.

https://arstechnica.com/civis/attachments/1772812012884-png.129830/

1772812012884.png

It is at max of 1,313 m/s for the LOI and the south pole landing sites are in those 1,000+ m/s circles. There is a reason Apollo landed in equatorial regions. The LOI for Apollo 11 was 900 m/s.

Now if it takes 1313 m/s to get into LLO then it will take 1313 m/s to get back out. So we are talking 2,626 m/s. Throw in a couple hundred m/s for docking, course corrections (burns are never perfect) and safety margin and 3,000 m/s is a reasonable budget. You can reduce DeltaV somewhat by having a long loiter in LLO which reduces the prohibitive cost of a plane change by coasting up to the apolune (the same way GEO sats coast up to apogee in a GTO orbit but you now largely erased the big advantage of LLO over NRHO in that it is faster for crew missions.

Apollo did consider a polar landing for one of the late Apollo missions but it was canceled due to the higher risk of LoM and LoC. To get the margins needed the Apollo CSM would need to dwell in an intermediate orbit for an extra 2.8 days on the LOI and 1.6 days on the TEI. So an extra four days to the mission timeline. Technically Orion with its 1.3 km/s DeltaV "could" get to Polar LLO but it would require a loiter time of ... 6 days. That is 6 days on the way in and another 6 on the way out. You could make it asymmetrical to reduce risk like Apollo did but it would still be around 12 days loiter on top of 6 days transit on top of 6+ days surface mission.

For reusable landers LLO has another issue. It is so deep in the moon gravity well that while the lander itself uses less propellant you have to bring propellant to the lander. The propellant you bring to the lander requires more DeltaV so that propellant is requiring more propellant. So your lander uses less prop but yout tug/tanker uses more. Total prop usage per mission increases not decreases. A crew landing is essentially all propellant on a first order simplification.

TLDR: NASA knows what they are doing. NRHO got maligned by its association with porkish SLS & Orion (even by me in the past). NRHO is not a terrible orbit for a reusable architecture. It has numerous advantages to include that it is very cold. That is important if you have reusable cryogenic landers trying to minimize boiloff waiting months for crews to arrive. Your lander will point its nose at the sun to reduce thermal load. However in LLO like LEO the moon is a thermal mirror. Thermal load is substantially worse. Using NRHO as a staging point does not require a gateway station.

Even in the analysis above the alternate orbit is all around worse except saving 3% to 6% prop.

SPACE JELLYFISH PREDICTOR

“Accessing and remediating any of these issues can only be performed in the VAB.” //

normally butters Ars Praefectus
19y
5,319

georges said:
It's amazing to me that there isn't a retractable maintenance arm on the launch stand. The ground hardware all cost sooooo much money but no one though to add this?

Apollo had a Mobile Service Structure at each pad.
Shuttle had a Rotating Service Structure at each pad.

Ares/SLS were based on the Clean Pad concept. NASA wanted commercial launch providers to agree to use the pads at LC-39 (as well as the VAB, crawler-transporters, and crawlerway infrastructure) between NASA exploration missions. Each launch vehicle type from each launch provider would have its own Mobile Launcher Platform including the umbilical tower. There weren't going to be any vehicle-specific support structures, just a clean pad to share.

During Ares V development, rollout weight became a major concern. Unlike Saturn V, Ares V and SLS have huge SRBs loaded with massive amounts of solid propellant. The weight of the stack including the launch platform, umbilical tower, and crawler was pushing the limits of what the crawlerway foundations can support. They were worried it would be so heavy that it would sink into the Florida swamp on the way to the pad.

These factors contributed to the (poor) design choice to minimize the scope of the umbilical tower and rely heavily on the VAB for service access. //

aggressive-trail Smack-Fu Master, in training
1m
85

woodbourne said:
Time to cancel the program. There's nothing on the moon that we need right now. Let the Chinese waste the money on useless rockets and wait for there to be an economic reason for going there. We're basically using technology from the 1940's to accomplish something that has no economic payback using the same corrupt defense contractors and the same stupid procurement rules that we had 60 years ago. Enough, please stop this project.

And here I was, thinking that these arguments from the 60s would have been settled by now. Beyond the fact that the economic case for Luna can be quantifiably justified today, I’d argue the biggest argument is what it provides us in terms of science.

The far side of the moon is shielded from Earth’s radio interference, making it the most valuable real estate in the solar system for radio astronomy and deep space communication infrastructure.

Scientists want to build LF radio telescopes there to detect signals from the "Dark Ages", the period after the Big Bang but before the first stars formed. These signals are blocked by Earth’s ionosphere. This environment is also perfect for tracking deep-space objects without local interference.

If you don’t care about anything else, at least care about that. //

rhgedaly Ars Scholae Palatinae
8y
1,290
First hydrogen, then helium. Hope the batteries that will need recharging aren't lithium. Damn the periodic table! //

Chuckstar Ars Legatus Legionis
23y
37,070
Subscriptor

dehildum said:
That table gives them 100+ reasons for launch delays and more profits for the contractors.

I don’t remember any Apollo, Gemini, or Mercury vehicle needing to be returned to the VAB….

Apollo 16 was moved back to the VAB, after a fuel tank in the service module was damaged during testing (over-pressurized).

But the reason that was the only time they had to do that in Apollo was not because the Saturn was so much better designed, but because the Mobile Service Structure provided access to the full stack, and they only needed the VAB if a repair required taking the stack apart, which was necessary for the Apollo 16 repair.

All the assembly/integration at the Cape for Gemini and Mercury were done on the launch stand. The VAB was purpose-built for Apollo-Saturn. //

MilesArcher Ars Centurion
5y
294
Subscriptor
BCGeiger said:
🎼Hanger Queen, 🎶
🎼Should’a cancelled it back in ‘17🎶
🎼Hanger Queen🎶
🎼They keep pouring cash into this bad machinee🎶
Man, you had the opportunity to rhyme hydrazine and missed it.

Yui Smack-Fu Master, in training
5m
81
The most astonishing part of Jared's letter is that while Butch and Suni were on station they were advocating for NASA to show leadership, and yet disagreements on the ground had "deteriorated into unprofessional conduct".

Yikes. //

Wickwick Ars Legatus Legionis
15y
39,338
dangle said:
Yeah, but we remember that at the time, after we were still blinking in disbelief at our screens after formal coverage of the test flight finished, and after an hour delay to the presser in order to get their stories straight, that when the feed returned, Jim Bridenstine stared into the camera and confidently announced that "Today, a lot of things went right."
I will react today exactly as I did in the comments of that the article that covered that: Taht was Bridenstine being a good politician and saving as much face for a valued contractor as he could. His words didn't matter. What would matter was his (and NASA's) actions. And as it turns out, the actions were spot-on. NASA forced Boeing to refly OFT-1.

Unfortunately, Ballast Bill Nelson was the Administrator after the OFT-1 repeat and he has a long history with Boeing and Old Space in general. And it was under his watch that the OFT-1 repeat was accepted as sufficient even though there were thruster issues again.

NASA owned up to not monitoring Boeing closely enough prior to the OFT-1 launch. However, they at least did the right thing and made Boeing repeat the test. NASA performed far more poorly when human life was on the line for OFT-2. //

https://planet4589.org/space/misc/starliner26.ji.pdf
https://planet4589.org/space/misc/starliner26.pdf

“The most troubling failure revealed by this investigation is not hardware.”

NASA on Thursday announced it has formally classified the 2024 crewed flight of the Starliner spacecraft as a “Type A” mishap, an acknowledgement that the test flight was a serious failure. //

The letter and a subsequent news conference on Thursday afternoon were remarkable for the amount of accountability taken by NASA. Moreover, at Isaacman’s direction, the space agency released an internal report, comprising 311 pages, that details findings from the Program Investigation Team that looked into the Starliner flight.

“Starliner has design and engineering deficiencies that must be corrected, but the most troubling failure revealed by this investigation is not hardware,” Isaacman wrote in his letter to the NASA workforce. “It is decision-making and leadership that, if left unchecked, could create a culture incompatible with human spaceflight.”

Isaacman said there would be “leadership accountability” as a result of the decisions surrounding the Starliner program, but did not say which actions would be taken. //

The true danger the astronauts faced on board Starliner was not publicly revealed until after they landed and flew back to Houston. In an interview with Ars, Wilmore described the tense minutes when he had to take control of Starliner as its thrusters began to fail, one after the other.

Essentially, Wilmore could not fully control Starliner any longer. But simply abandoning the docking attempt was not a palatable solution.

NASA shall evaluate the “viability of transferring the ISS to a safe orbital harbor” after retirement. //

The most recent NASA authorization act, passed in 2022, extended the US government’s support for the ISS program until 2030. The amendment tacked onto this year’s bill would not change the timeline for ending operations on the ISS, but it asks NASA to reconsider its decision about what to do with the complex after retirement.

The amendment would direct NASA to “carry out an engineering analysis to evaluate the technical, operational, and logistical viability of transferring the ISS to a safe orbital harbor and storing the ISS in such harbor after the end of the operational low-Earth orbit lifetime of the ISS to preserve the ISS for potential reuse and satisfy the objectives of NASA.” //

In 2024, NASA awarded SpaceX a nearly $1 billion contract to develop a souped-up version of its Dragon spacecraft, which would be equipped with additional thrusters and propellant tanks to provide the impulse required to steer the space station toward a targeted reentry. The deorbit maneuvers will slow the station’s velocity enough for Earth’s gravity to pull it back into the atmosphere. //

Artist’s illustration of SpaceX’s deorbit vehicle, based on the design of the company’s Dragon spacecraft. The modified spacecraft will have 46 Draco thrusters—30 for the deorbit maneuvers and 16 for attitude control. Credit: SpaceX //

The deorbit vehicle needs to slow the station’s speed by about 127 mph (57 meters per second), a tiny fraction of the spacecraft’s orbital velocity of more than 17,000 mph (7.7 kilometers per second). But the station mass is around 450 tons (400 metric tons), equivalent to two freight train locomotives, and measures about the length of a football field. Changing its speed by just 127 mph will consume about 10 tons (9 metric tons) of propellant, according to a NASA analysis released in 2024.

The analysis document shows that NASA considered alternatives to discarding the space station through reentry. One option NASA studied involved moving the station into a higher orbit. At its current altitude, roughly 260 miles (420 kilometers) above the Earth, the ISS would take one to two years to reenter the atmosphere due to aerodynamic drag if reboosts weren’t performed. NASA does not want the space station to make an uncontrolled reentry because of the risk of fatalities, injuries, and property damage from debris reaching the ground.

Boosting the space station’s orbit to somewhere between 400 and 420 miles (640 to 680 kilometers) would require a little more than twice the propellant (18.9 to 22.3 metric tons) needed for deorbit maneuvers, according to NASA’s analysis. At that altitude, without any additional boosts, NASA says the space station would likely remain in orbit for 100 years before succumbing to atmospheric drag and burning up. Going higher still, the space station could be placed in a 1,200-mile-high (2,000-kilometer) orbit, stable for more than 10,000 years, with about 146 tons (133 metric tons) of propellant.

There are two problems with sending the ISS to higher altitudes. One is that it would require the development of new propulsive and tanker vehicles that do not currently exist, according to NASA. //

BobDole11 Ars Centurion
4y
290
I think everyone would love to see the ISS saved for posterity. I would imagine the grand kids of today's generation, when space flight may perhaps be common, visiting and touring a monument ISS and learning how primitive it was (compared to a +50'ish years future) and the bravery of the souls that ventured forth for the expansion of humanity's knowledge, science, exploration, cooperation, and greatness.

I've had those feelings and thoughts myself when viewing Apollo era hardware long ago. Standing by a Saturn 5 dwarfing my 8yr old stature filled me with inspiration to learn about spaceflight, science, and engineering.

But - the ramifications of a collision (or collisions) with space junk yielding 450 tons of more space junk, yielding further collisions and more and smaller junk, and on and on is just too great. The debris at a higher orbit takes too long to deorbit. The thought of our orbitals becoming impassable for centuries is terrifying. //

Veritas super omens Ars Legatus Legionis
13y
26,080
Subscriptor++
What would it take? Based on the history of the SLS I would predict it would take an order of magnitude more money than whatever NASA says and 20 to 30 years longer. There are many laudable goals for space missions, this isn't one of them!. //

fl4Ksh Ars Tribunus Militum
8y
1,518
Subscriptor
NASA is paying SpaceX $2.9B to develop a Starship lunar lander. That work has been ongoing since late 2021 and is scheduled to launch in late 2028.

That lunar lander design could be a pattern for a Starship LEO space station, which would have 1000 cubic meters of pressurized volume (ISS has 913), would support a crew of 10 (ISS supports 7), would be deployed to LEO in a single Starship launch (ISS required 12 years [1999 to 2011] and 35 launches), and would cost ~$10B (ISS cost $150B to build and deploy to LEO and $3B to $4B per year to operate, in today's money). Like the ISS, that Starship LEO space station would use cargo Dragon and crew Dragon spacecraft for resupply of consumables and for crew rotation.

That Starship LEO space station could be built in 36 months and launched in 2030.

Slow Launch System

“You know, you’re right, the flight rate—three years is a long time.”

jack1983 Smack-Fu Master, in training
12y
93

The Lurker Beneath said:
Do it on a windy day?
There are risks with too high wind speeds as well. High airflow causes static buildup and turbulence. Hydrogen requires very little ignition energy (well below 1mJ at stoichiometric conditions). So even a gust of wind can set off a combustible mixture.

Cryogenic hydrogen is an absolute nightmare to work with.

paulfdietz Ars Scholae Palatinae
7y
1,168
Using hydrogen as the fuel in the first stage was never a good idea. The density is just terrible, making the first stage much larger. Because the first stage is disposed of so quickly, Isp is less important; what's more important is "density impulse" (density x Isp), and LoX/LH2 is inferior to LOX/hydrocarbon by that metric.

Low density also makes the engines more expensive, as more pumping power is needed for a given thrust. //

paulfdietz Ars Scholae Palatinae
7y
1,168

pokrface said:
Right, but the "first stage" of SLS (and STS) is properly the SRBs.
It's more like the first "half stage". What matters for the argument is the velocity at which a stage is done. Even with the SRBs there, that's not that high (although higher than say the Falcon 9, which ends the stage 1 burn at an unusually low velocity so it can be recovered.)

The SRBs do allow the thrust of those LH2 engines to be somewhat lower, since they don't have to lift the fully fueled stack off the pad themselves. By the time the SRBs drop some propellant is gone. This ameliorates to some extent the relatively poor thrust/weight ratio of the engines (73.1 vs 184 for the Merlin 1D.)

While Rocketdyne’s ownership merry-go-round kept spinning, the company’s competitors pushed forward. SpaceX and Blue Origin, backed by wealthy owners, took a fresh approach to designing rockets. Apart from the technical innovations that led to reusable rockets, these newer companies emphasized vertical integration to cut costs and minimize reliance on outside supply chains. They wanted to design and build their own rocket engines and were not interested in outsourcing propulsion. Rocketdyne’s business was—and still is—entirely focused on selling ready-made engines to customers.

The launch startups that followed in the footsteps of SpaceX and Blue Origin have largely imitated their approach to insourcing. There are at least nine medium to large liquid-fueled rocket engines in production or in advanced development in the United States today, and just one of them is from the enterprise once known as Rocketdyne: the RS-25 engine used to power the core stage of NASA’s Space Launch System (SLS) rocket. //

The RS-25 engine, by far the largest in L3Harris’ portfolio and a former Rocketdyne product, is not part of the sale. The RS-25 was initially known as the Space Shuttle Main Engine and was designed for reusability. The expendable heavy-lift SLS rocket uses four of the engines, and NASA is burning through the 16 leftover shuttle-era RS-25 engines on the first four SLS flights for the agency’s Artemis Moon program. The second SLS flight is set to launch in the coming months on a mission carrying four astronauts beyond the Moon.

L3Harris will retain total ownership of the RS-25 program. The company has a contract with NASA to build new RS-25 engines for SLS flights beyond Artemis IV. But the new RS-25s will come at an expense of about $100 million per engine, significantly more than SpaceX sells an entire launch on a Falcon 9 rocket. The engine contract is structured as a cost-plus contract, with award and incentive fees paid by the government to L3Harris.

Looking west from Tucson, Arizona, USA one day last month, the sunset sky looked strange when it briefly lit up with the plume of a rocket launched from California a few minutes earlier. Appearing at times like a giant space fish, the impressive rocket launch from Vandenberg Air Force Base near Lompoc, California, was so noticeable because it was backlit by the setting Sun.