How Does a Gravitational Slingshot Work?
You've probably watched this sort of science-fiction scene more than once: some stalwart starship captain and their crew are fleeing from aliens/escaping a supernova /running out of fuel and are seemingly out of options, about to get eaten/vaporized/stuck. But then, just ahead, they spot a planet! So they head right for it, rockets blazing, then dive down and use its gravity to slingshot to safety. Hooray! Cue the triumphant music.
So it goes on the silver screen, at least. But does this maneuver work in real life?
Yes! Well, not so much the way it's done in movies—but it is an actual thing. It's widely known as a gravitational slingshot, though most scientists refer to it as a gravitational assist, and it's an essential tool for most interplanetary missions.
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
The idea seems simple enough. As a spacecraft approaches a massive object, say, a planet, the gravity of the planet bends its trajectory, changing the spacecraft's direction. But there's more to it than that: the spacecraft can actually use the planet's gravity to speed up or slow down after this maneuver, allowing easier voyages to the outer or inner planets, respectively.
While the trajectory-bending part seems obvious enough, that speed-up-or-slow-down part is pretty counterintuitive. It's related to the symmetry of gravity.
If you hold a rubber ball some distance from the ground and drop it, the ball will accelerate as it falls, speeding up until impact. Then it bounces, moving upward and decelerating as it does so. It will eventually come to a stop, whereupon you can catch it or let it fall again. But either way, it can't bounce any higher than the height from which you dropped it. It gained kinetic energy—the energy of motion—as it fell but then lost it once again postbounce as it slowed on its way back up. This action is symmetric, so at best (if you had a perfectly elastic ball and did this experiment in a vacuum), it would bounce to the same height from which you dropped it.
The same is true for a spacecraft approaching a planet. The world's gravity will accelerate you as you fall in, you'll whip around at closest approach (that's the 'slingshot' part), and then you'll lose that extra velocity as you move away because the planet's gravity is still pulling on you. As that gravitational grip slips away, the spacecraft will be moving relative to the planet at the same speed at which it initially approached.
So if all the bonus speed is lost on the way out, how can this maneuver be used to accelerate a spacecraft? The key is in the phrase 'relative to the planet.' If you approach the planet at, say, 20 kilometers per second (km/s), you'll leave with the same speed. But that's your speed measured against the planet.
At that same time, crucially, the planet is also orbiting the sun. If you approach the planet from behind (that is, in the direction of its motion), then, as the planet's gravity gives you a boost, it also, in a heliocentric sense, pulls you along, adding some of its orbital velocity to yours. That gives you a kick relative to the sun, speeding you up on your way to your destination. In essence, the spacecraft gets a net gain in speed by stealing a little bit of the planet's orbital kinetic energy.
In turn, this means the planet actually slows a bit in its orbit around the sun—which sounds dangerous! But fear not: the planet slows in proportion to how much more massive it is than the spacecraft. Given a typical one-ton probe compared with a multisextillion-ton world, the planet doesn't noticeably slow at all. You could launch a million probes at it and never be able to tell the difference in its orbital speed. A bacterium bouncing off you while you're out walking would have a far larger effect on you.
The reason it's worthwhile to go to the trouble of gravitational assists is that spacecraft are launched by rockets, which can only accelerate to some top speed. For our current rocketry, these speeds are so low and the interplanetary distances so great that even the fastest, most direct voyages take years (or even decades for destinations in the outer solar system). You can load the spacecraft with more fuel to burn to go faster, but there's a limit to that, too. Fuel has mass, and you'd need to accelerate that extra mass, which takes more fuel, which has more mass. This catch-22 is described by what is called the rocket equation, and it means the amount of fuel you must add to move even slightly faster reaches prohibitive scales very quickly.
So shaving time off your voyage requires some other method—such as siphoning speed from a big, juicy planet along the way! For example, the Cassini probe to Saturn, which launched in 1997, was a huge spacecraft, the size of a school bus, and had a mass of 2.5 metric tons without fuel. (The addition of the fuel it needed to fulfill its mission at Saturn, along with the launch vehicle and other equipment, tipped the scales to 5.7 metric tons.) It would've taken practically forever to get to Saturn with the rockets we had then. So the mission planners took advantage of Jupiter, sending the spacecraft past it on a speed-boosting slingshot maneuver that shaved significant time off the journey. In fact, just to get out to Jupiter in the first place, Cassini also performed two fuel-saving flybys of Venus and one of Earth, stealing planetary orbital energy every time.
A gravitational assist works the other way, too. Earth orbits the sun at more than 30 km/s, so firing a probe at the sun or the inner planets is extremely hard because of all that sideways velocity. Instead mission planners prefer a more circuitous route. They launch the spacecraft with enough velocity in the opposite direction of Earth's path around the sun to drop in front of, say, Venus, where it can then donate some of its orbital energy to the planet to drop toward the sun even more. BepiColombo, a joint European Space Agency and Japan Aerospace Exploration Agency mission to Mercury, did exactly this, passing Earth once and Venus twice to get in Mercury's vicinity. Even then, it had to do a total of six gravity assists past Mercury to match the planet's orbital speed around the sun. The last assist was in January 2025, and it will enter Mercury orbit in November 2026.
Gravitational assists are an emblematic example of why space travel is hard —it is exactly rocket science, after all. Gravity is the biggest culprit; just getting away from Earth in the first place is the largest part of the problem. It's ironic, then, that gravity can make reaching most of the rest of the solar system so much easier.
Hashtags
Try Our AI Features
Explore what Daily8 AI can do for you:
Comments
No comments yet...
Related Articles
Associated Press
21 minutes ago
- Associated Press
Novo Nordisk advances early-stage obesity medication, amycretin, to phase 3 clinical development based on early-phase clinical trial results in people with obesity or excess weight, published in The Lancet
PLAINSBORO, N.J., June 20, 2025 /PRNewswire/ -- Today, results from two early-phase clinical trials evaluating Novo Nordisk's amycretin, an innovative investigational obesity treatment designed to target appetite regulation, were published in The Lancet.1 In a phase 1b/2a clinical trial of 125 adults with overweight or obesity, once-weekly subcutaneous amycretin appeared to be safe and tolerable in trial participants, who also achieved significantly greater weight loss across the full range of doses investigated versus placebo.1 A related phase 1 trial of once-daily oral amycretin in adults with obesity or overweight also showed that treatment was safe and tolerable with an observed reduction in body weight compared to placebo.2 No weight loss plateau was observed in either trial at the end of the respective treatment durations.1,2 Data on subcutaneous amycretin is scheduled to be presented on Sunday, June 22nd, during a late-breaking poster session at the American Diabetes Association's® (ADA) 85th Scientific Sessions.1 'We are pleased with the promising results of amycretin and the feedback from regulatory authorities and are excited to advance both subcutaneous and oral versions of this molecule into phase 3 development for weight management. At Novo Nordisk, we understand that addressing obesity is a complex challenge that many patients face. These results reflect our robust pipeline in obesity, our focus on progressing scientific innovation and expanding the range of options available to patients and healthcare professionals,' said Martin Holst Lange, executive vice president for Development at Novo Nordisk. 'We remain steadfast in our mission to discover and develop therapies that can have a meaningful impact in the lives of those affected by obesity.' Results from the phase 1b/2a trial of subcutaneous amycretin showed treatment-emergent adverse events (TEAEs) were mild or moderate in severity and increased in frequency in a dose-dependent manner. The most frequent reported TEAEs were gastrointestinal in nature. Compared to placebo, participants receiving amycretin observed greater weight loss across the full range of doses investigated.1 Subcutaneous amycretin at multiple doses demonstrated greater weight reduction than placebo at the end of the trial. Participants who received the highest doses (up to 60 mg) reported body weight reductions of up to 24.3% versus 1.1% with placebo after 36 weeks of treatment. Results from this first-in-human phase 1b/2a study support further investigation of potential weight-loss efficacy of amycretin. Results from the published phase 1 trial of oral amycretin showed that the most common TEAEs were related to gastrointestinal symptoms (mainly nausea and vomiting) and decreased appetite; these were most frequent for the higher doses. Trial participants receiving the study treatment demonstrated significantly greater weight loss across the full range of doses investigated versus the placebo group.2 Exploratory results showed participants taking 100 mg per day of oral amycretin achieved a mean weight loss of 13.1% versus 1.2% with placebo after 12 weeks.2 Based on these phase 1 results, longer evaluation with more participants is warranted to substantiate the full efficacy findings of oral amycretin on body weight reductions and changes in metabolic parameters. Novo Nordisk will advance both subcutaneous and oral amycretin formulations straight to phase 3 development for weight management based on these and other completed clinical studies, as well as feedback received from regulatory authorities. About amycretin Amycretin is a unimolecular long-acting GLP-1 and amylin receptor agonist under development by Novo Nordisk, to provide a treatment for adults with overweight or obesity and as a treatment for adults with type 2 diabetes. Amycretin is under investigation for oral and subcutaneous administration, and is not approved in the US for weight loss. About the phase 1b/2a subcutaneous amycretin trial The phase 1b/2a trial was a randomized, placebo-controlled, single-center, double-blinded study of 125 participants assessing the safety, tolerability, pharmacokinetics, and effects on body weight after subcutaneous administration of amycretin in people with overweight or obesity.1 Adults with a body mass index of 27-39.9kg/m2 and glycated hemoglobin (HbA1c) <6.5% were eligible for the trial.1 The trial was conducted in 5 parts: a single ascending dose (Part A) for determination of pharmacokinetics and starting dose for the first multiple dose cohort in which the safety and tolerability were explored using dose escalation until 36 weeks of total treatment duration (Part B).1 Lastly, in the multiple ascending dose – dose response parts, body weight loss was explored for up to 36 weeks of dosing by escalating to dose levels of 1.25 mg, 5 mg, and 20 mg, respectively, dosed for 12 weeks (Part E, D and C).1 About the phase 1 oral amycretin trial The phase 1 single-center, randomized, placebo-controlled study evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of single ascending doses (Part A) and multiple ascending doses (Part B, 10 days of treatment; Part C/D, 12 weeks of treatment) of 144 adult participants with overweight or obesity.2 The primary endpoint was the number of treatment-emergent adverse events (TEAEs) observed in the trial. The trial evaluated the single-ascending dose and multiple ascending doses for oral amycretin, up to 2 times 50 mg, in people with overweight or obesity, with a total treatment duration of up to 12 weeks.2 About obesity Obesity is a serious chronic, progressive, and complex disease that requires long-term management.3-5 One key misunderstanding is that this is a disease of just lack of willpower, when in fact there is underlying biology that may impede people with obesity from losing weight and keeping it off.3,5 Obesity is influenced by a variety of factors, including genetics, social determinants of health, and the environment.6,7 The prevalence of overweight and obesity is a public health issue that has severe cost implications to healthcare systems.8,9 In the US, about 40% of adults live with obesity.10 About Novo Nordisk Novo Nordisk is a leading global healthcare company that's been making innovative medicines to help people with diabetes lead longer, healthier lives for more than 100 years. This heritage has given us experience and capabilities that also enable us to drive change to help people defeat other serious chronic diseases such as obesity, rare blood, and endocrine disorders. We remain steadfast in our conviction that the formula for lasting success is to stay focused, think long-term, and do business in a financially, socially, and environmentally responsible way. With a US presence spanning 40 years, Novo Nordisk US is headquartered in New Jersey and employs over 10,000 people throughout the country across 12 manufacturing, R&D and corporate locations in eight states plus Washington DC. For more information, visit Facebook, Instagram, and X. Novo Nordisk is committed to the responsible use of our semaglutide-containing medicines which represent distinct products with different indications, dosages, prescribing information, titration schedules, and delivery forms. These products are not interchangeable and should not be used outside of their approved indications. Learn more at Contacts for further information References © 2025 Novo Nordisk All rights reserved. US25SEMO01477 June 2025 View original content to download multimedia: SOURCE NOVO NORDISK INC.
Associated Press
21 minutes ago
- Associated Press
MountBay Energy Unlocks Microbial Biofilm Technology to Revolutionize Battery Longevity
NEW YORK, June 21, 2025 (GLOBE NEWSWIRE) -- MountBay Energy has unveiled groundbreaking research on microbial biofilms that could redefine the future of grid-scale energy storage. The study, led by founder Vrushabhraj Tanawade, introduces a bio-integrated insulation method using thermophilic and mesophilic microbial consortia to regulate heat inside battery modules. The results are striking: up to a 22% reduction in internal temperature and a 30% improvement in carbon lifecycle efficiency. 'This innovation is about biology meeting infrastructure,' says Tanawade. 'We've discovered how nature's mechanisms can dramatically extend the life of our clean energy systems.' Unlike conventional synthetic cooling solutions, MountBay's microbial approach is circular, biodegradable, and scalable—opening up new frontiers for climate resilience and fire-risk reduction in hot environments. The research aligns perfectly with MountBay's mission to power the AI economy through clean, sustainable, and advanced infrastructure. It also positions the company as a frontrunner in biological material integration across the energy sector. Additionally, MountBay has released a preliminary transformative feasibility report for a Lunar Solar Belt—a continuous solar array on the Moon that can beam uninterrupted, clean energy back to Earth. The report outlines how in-situ resource utilization (ISRU), autonomous lunar robotics, and microwave power transmission could enable the construction of a moon-based solar plant by the 2030s. With an energy return on investment (EROI) of 8:1, the system offers a scalable, emission-free solution to humanity's growing power demands. 'This is not just an energy project—it's a civilization-scale investment in global stability,' said Tanawade. 'We believe the Moon should be a cooperative utility, not a geopolitical race.' MountBay is also proposing a new diplomatic framework—The Earth-Moon Energy Accord (EMEA)—to ensure equitable access, safety, and international cooperation. The concept directly supports MountBay's mission: to push the frontiers of clean power while securing energy independence for AI-driven economies. Tanawade is rallying governments, institutions, and innovators to join him. 'It's time for America to lead the most ambitious energy project in human history,' he said. Media Contact: Vrushabhraj Tanawade Founder @ MountBay Energy Contact : [email protected] Website: Linkedin: Linkedin - Vrushabhraj T Disclaimer: This press release is provided by MountBay Energy. The statements, views, and opinions expressed are solely those of the provider and do not necessarily reflect those of this media platform or its publisher. Any names or brands mentioned are used for identification purposes only and remain the property of their respective owners. No endorsement or guarantee is made regarding the accuracy, completeness, or reliability of the information presented. This material is for informational purposes only and does not constitute financial, legal, or professional advice. Readers are encouraged to conduct independent research and consult qualified professionals. The publisher is not liable for any losses, damages, or legal issues arising from the use or publication of this content. Photos accompanying this announcement are available at:
Hypebeast
28 minutes ago
- Hypebeast
Map the Cosmos on Your Wrist With HVILINA's Universum Cosmographia Wristwatch
Summary HVILINA's newly unveiled Universum Cosmographia is a timepiece that artfully fuses historical astronomy with modern horology. Drawing inspiration from medieval star maps and modern planetary science, the watch features a three-dimensional planetarium and a GMT disc styled after a 9th-century celestial chart. Developed in collaboration with Professor Richard Kerner, a Sorbonne physicist and medieval cartography expert, the project bridges ancient cosmological worldviews with present-day innovation. Housed in a stainless steel case with a redesigned bezel and caseback, the watch is protected by sapphire crystals on both sides, complete with a 50-meter water resistance. At its core lies a meticulously crafted 3D model of the Solar System, where miniature stylized planets appear to float in zero gravity. Guilloché engraving enhances the multi-layered dial, adding depth and a sense of celestial movement. Above the planetary display, a rotating GMT disc unveils a medieval star map through a sculpted aperture. Meanwhile, Latin inscriptions of zodiac constellations unfold in a 24-hour cycle, with contrasting light and dark halves indicating the day and timepiece is powered by the Miyota 9075 Premium automatic movement, delivering GMT functionality, a 42-hour power reserve and a daily accuracy of -10/+30 seconds. The movement's rotor is engraved with trans-Neptunian objects. This includes the oval-shaped dwarf planet Haumea, thus reinforcing the astronomical theme. Available in four colorways, each limited to 500 pieces, the Universum Cosmographia comes fitted with a quick-release rubber strap with optional upgrades such as a leather strap, personalized serial number, or a custom GMT disc featuring the wearer's zodiac sign. Priced at €400 EUR (approx. $461 USD), the timepiece is now available for pre-order via HVILINA'swebstore. The timepiece will be officially released in November, 2025.
