If you’ve ever dealt with orbital mechanics or sophisticated computer graphics, you’ve probably run across the math term quaternions. [Anyleaf] has a guide to the practical use of this math concept which focuses more on practicality than theory. We like it!
Quaternions are one of at least two ways to model rotations in a 3D space. Most people are familiar with the classic Euler angles which cover yaw, pitch, and roll. However, this method is prone to some ambiguities — in other words, there are multiple ways to go from one Euler state to another and all are equally valid. In addition, Euler angles are prone to gimbal lock where two of the axes are parallel and, thus, don’t have a different effect on the object’s orientation. There are several ways to combat that including the use of quaternions.
When Astra’s diminutive Rocket 3.3 lifted off from its pad at the Cape Canaveral Space Force Station on June 12th, everything seemed to be going well. In fact, the mission was progressing exactly to plan right up until the end — the booster’s second stage Aether engine appeared to be operating normally until it abruptly shut down roughly a minute ahead of schedule. Unfortunately, orbital mechanics are nothing if not exacting, and an engine burn that ends a minute early might as well never have happened at all.
According to the telemetry values shown on-screen during the live coverage of the launch, the booster’s upper stage topped out at a velocity of 6.573 kilometers per second, well short of the 7.8 km/s required to attain a stable low Earth orbit. While the video feed was cut as soon as it was clear something had gone wrong, the rigid physics of spaceflight means there’s little question about the sequence of events that followed. Without the necessary energy to stay in orbit, the upper stage of the rocket would have been left in a sub-orbital trajectory, eventually reentering the atmosphere and burning up a few thousand kilometers downrange from where it started.
An unusual white plume is seen from the engine as it shuts down abruptly.
Of course, it’s no secret that spaceflight is difficult. Doubly so for startup that only has a few successful flights under their belt. There’s no doubt that Astra will determine why their engine shutdown early and make whatever changes are necessary to ensure it doesn’t happen again, and if their history is any indication, they’re likely to be flying again in short order. Designed for a Defense Advanced Research Projects Agency (DARPA) competition that sought to spur the development of cheap and small rockets capable of launching payloads on short notice, Astra’s family of rockets have already demonstrated unusually high operational agility.
Astra, and the Rocket 3.3 design, will live to fly again. But what of the payload the booster was due to put into orbit? That’s a bit more complicated. This was the first of three flights that were planned to assemble a constellation of small CubeSats as part of NASA’s TROPICS mission. The space agency has already released a statement saying the mission can still achieve its scientific goals, albeit with reduced coverage, assuming the remaining satellites safely reach orbit. But should one of the next launches fail, both of which are currently scheduled to fly on Astra’s rockets, it seems unlikely the TROPICS program will be able to achieve its primary goal.
So what exactly is TROPICS, and why has NASA pinned its success on the ability for a small and relatively immature launch vehicle to make multiple flights with their hardware onboard? Let’s take a look.
On a dark night in 2006 I was bicycle commuting to my office, oblivious to the countless man made objects orbiting in the sky above me at thousands of miles per hour. My attention was instead focused on a northbound car speeding through a freeway underpass at dozens of miles per hour, oblivious to my southbound headlamp. The car swerved into the left turn lane to get to the freeway on-ramp. The problem? I was only a few feet from crossing the entrance to that very on-ramp! As the car rushed through their left turn I was presented with a split second decision: slow, and possibly stop in the middle of the on-ramp, or just go for it and hope for the best.
In Blue: Terrified cyclist. In Red: A speeding car careening around a corner without slowing down.
By law I had the right of way. But this was no time to start discussing right of way with the driver of the vehicle that threatened to turn me into a dark spot on the road. I followed my gut instinct, and my legs burned in compliance as I sped across that on-ramp entrance with all my might. The oncoming car missed my rear wheel by mere feet! What could have ended in disaster and possibly even death had resulted in a near miss.
Terrestrial vehicles generally have laws and regulations that specify and enforce proper behavior. I had every right to expect the oncoming car be observant of their surroundings or to at least slow to a normal speed before making that turn. In contrast, traffic control in Earth orbit conjures up thoughts of bargain-crazed shoppers packed into a big box store on Black Friday.
So is spacecraft traffic in orbit really a free-for-all? If there were stringent rules, how can they be enforced? Before we explore the answers to those questions, let’s examine the problem we’re here to discuss: stuff in space running into other stuff in space.
Fans of the lusciously voiced space aficionado [Scott Manley] will know he often uses Kerbal Space Program (KSP) in his videos to knock together simple demonstrations of blindingly complex topics such as orbital mechanics. But as revealed in one of his recent videos, YouTube isn’t the only place where his KSP craft can be found these days. It turns out he used his virtual rocket building skills to help the creators of Netflix’s Stowaway develop a realistic portrayal of a crewed spacecraft in a Mars cycler orbit.
The Mars cycler concept was proposed in 1985 by Buzz Aldrin as a way to establish a long-term human presence on the Red Planet. Put simply, it describes an orbit that would allow a vehicle to travel continuously between Earth and Mars while needing only an occasional engine burn for course corrections. The spacecraft couldn’t actually stop at either planet, but while it made a close pass, smaller craft could rendezvous with it to hitch a ride. The concept can be thought of as a sort of interplanetary train: where passengers and cargo are picked up and dropped off at “stations” above Earth and Mars. It’s worth noting that a similar cycler orbit should be possible for Earth-Venus trips, but nobody really wants to go there.
An early KSP proof of concept for Stowaway.
The writers of Stowaway wanted their film to take place on a Mars cycler, and to avoid having to create the illusion of weightlessness, they wanted their fictional craft to also have some kind of artificial gravity. The only problem was, they weren’t sure what that would actually look like. So they reached out to [Scott], who in turn used KSP to throw together a rough idea of how such a ship might work in the real-world.
As you can see in the video below, the CGI spacecraft shown in the film’s recently released trailer ended up bearing a strong resemblance to its KSP prototype. While naturally some artistic license was used, [Scott] is excited by what he’s seen so far. The spinning spacecraft, which uses a spent upper stage to counterbalance its crew module and features a stationery utility node at the center, certainly looks impressive; all the more so with the knowledge that it’s based on sound principles.
While Netflix has had a hand in some surprisingly realistic science fiction in the past, they’ve also greenlit some real groan-worthy productions (if you haven’t watched Away, don’t). So until we can see the whole thing for ourselves, we can only hope that [Scott]’s sage advice will allow the crew of Stowaway to fly safe.
Mars may not be the kind of place to raise your kids, but chances are that one day [Elton John]’s famous lyrics will be wrong about there being no one there to raise them. For now, however, we have probes, orbiters, and landers. Mars missions are going strong this year, with three nations about to launch their rockets towards the Red Planet: the United States sending their Perseverance rover, China’s Tianwen-1 mission, and the United Arab Emirates sending their Hope orbiter.
As all of this is planned to happen still within the month of July, it almost gives the impression of a new era of wild space races where everyone tries to be first. Sure, some egos will certainly be boosted here, but the reason for this increased run within such a short time frame has a simple explanation: Mars will be right around the corner later this year — relatively speaking — providing an ideal opportunity to travel there right now.
In fact, this year is as good as it gets for quite a while. The next time the circumstances will be (almost) as favorable as this year is going to be in 2033, so it’s understandable that space agencies are eager to not miss out on this chance. Not that Mars missions couldn’t be accomplished in the next 13 years — after all, several endeavors are already in the wings for 2022, including the delayed Rosalind Franklin rover launch. It’s just that the circumstances won’t be as ideal.
But what exactly does that mean, and why is that? What makes July 2020 so special? And what’s everyone doing up there anyway? Well, let’s find out!
When it comes to the quest for artifacts from the Space Race of the 1960s, few items are more sought after than flown hardware. Oh sure, there have been stories of small samples of the 382 kg of moon rocks and dust that were returned at the cost of something like $25 billion making it into the hands of private collectors, and chunks of the moon may be the ultimate collector’s item, but really, at the end of the day it’s just rock and dust. The serious space junkie wants hardware – the actual pieces of human engineering that helped bring an epic adventure to fruition, and the closer to the moon the artifact got, the more desirable it is.
Sadly, of the 3,000,000 kg launch weight of a Saturn V rocket, only the 5,600 kg command module ever returned to Earth intact. The rest was left along the way, mostly either burned up in the atmosphere or left on the surface of the Moon. While some of these artifacts are recoverable – Jeff Bezos himself devoted a portion of his sizable fortune to salvage one of the 65 F1 engines that were deposited into the Atlantic ocean – those left on the Moon are, for now, unrecoverable, and in most cases they are twisted heaps of wreckage that was intentionally crashed into the lunar surface.
But at least one artifact escaped this ignominious fate, silently orbiting the sun for the last 50 years. This lonely outpost of the space program, the ascent stage from the Apollo 10 Lunar Module, appears to have been located by a team of amateur astronomers, and if indeed the spacecraft, dubbed “Snoopy” by its crew, is still out there, it raises the intriguing possibility of scoring the ultimate Apollo artifact by recovering it and bringing it back home.
Things aren’t looking good for NASA’s Space Launch System (SLS). Occasionally referred to as the “Senate Launch System”, or even less graciously, the “Rocket to Nowhere”, the super heavy-lift booster has long been a bone of contention for those in the industry. Designed as an evolution of core Space Shuttle technology, the SLS promised to reuse existing infrastructure to deliver higher payload capacities and lower operating costs than its infamous winged predecessor. But in the face of increased competition from commercial launch providers and proposed budget cuts targeting future upgrades and expansions of the core booster, the significantly over budget and behind schedule program is in a very precarious position.
Which is not to say the SLS doesn’t look impressive, at least on paper. In its initial configuration it would easily take the title as the world’s most powerful rocket, capable of lifting nearly 105 tons into low Earth orbit (LEO), compared to 70 tons for SpaceX’s Falcon Heavy. It would still fall short of the mighty Saturn V’s 155 tons to LEO, but the proposed “Block 2” upgrades would increase SLS payload capability to within striking distance of the iconic Apollo-era booster at 145 tons. Since the retirement of the Space Shuttle in 2011, NASA has been adamant that the might of SLS was the only way the agency could accomplish bigger and more ambitious missions to the Moon, Mars, and beyond.
Or at least, they were. On March 13th, NASA Administrator Jim Bridenstine testified to Congress that in an effort to avoid further delays, the agency is exploring the possibility of sending their Orion spacecraft to the Moon with a commercial launcher. The statement came as a shock to many in the aerospace community, as it would seem to call into question the future of the entire SLS program. If commercial rockets can do the job of SLS, at least in some cases, why does the agency need it?
NASA is currently preparing a report which investigates what physical and logistical modifications would need to be made to missions originally slated to fly on SLS; a document which is sure to be scrutinized by SLS supporters and critics alike. Until the report is released, we can speculate about what this hypothetical flight to the Moon might look like.
