The top speed of military aircraft like the SR-72 is estimated and unsurprisingly classified, with officials saying only that it will be able to hit at least the minimum hypersonic speed of Mach 5, so we'll use that as our baseline.
In 2004, the uncrewed NASA X-43A set a speed record at Mach 9.6, or 7,310 mph at an altitude of about 110,000 feet. Knight set the record for fastest crewed flight in 1967 when he piloted the North American X-15 to Mach 6.72 (4,520 mph) at an altitude of 102,100 feet. Air Force and NASA when test pilot William J. Hypersonic speeds have been achieved before, most notably by the U.S. These things don't happen at one particular speed, so the term "hypersonic" instead refers to the point at which they start to meaningfully affect the mechanics of flight-generally accepted to be Mach 5, or 3,836.35 mph in conditions of 20 degrees Celsius at sea level. Generally, hypersonic speeds are the point at which the molecules of air that surround the aircraft start to change by breaking apart ( dissociation) and/or picking up electrical charge ( ionization). But while "supersonic" has the clear cut definition of being faster than the speed of sound (Mach 1), hypersonic is a little fuzzier. Hypersonic is, obviously, supersonic on steroids. It's all very impressive, but it can be hard to wrap your head around in the abstract, so let's do a little bit of napkin math to really bring it home.įirst, let's establish some terms. The hypersonic SR-72 is reported to be making great gains in secret. The United States is currently developing hypersonic missiles that travel in excess of 6,000 miles per hour. You can read the conference paper on the conference website.If you have a need for speed, the next frontier is hypersonic. They also plan to compare acoustic temperature readings to readings from other instruments to try to figure out the large fluctuations. The team plans to continue using SuperCam microphone data to observe how things like daily and seasonal variations might affect the speed of sound on Mars. This data can help fill in some of the blanks on Mars' rapidly changing planetary boundary layer. Given that any human astronauts traveling to Mars anytime soon will need to be wearing pressurized spacesuits with comms equipment, or living in pressurized habitat modules, this is unlikely to pose an immediate problem – but it could be a fun concept for science-fiction writers to tinker with.īecause the speed of sound changes due to temperature fluctuations, the team was also able to use the microphone to measure large and rapid temperature changes on the Martian surface that other sensors had not been able to detect. This could lead to what the researchers call a "unique listening experience" on Mars, with higher-pitched sounds arriving sooner to the listener than lower ones. The result of this is that sound travels more than 10 meters per second faster at higher frequencies than it does at low ones. Chide and his team measured the time between the laser firing and the sound reaching the SuperCam microphone at 2.1 meters altitude, to measure the speed of sound at the surface.Īt frequencies above 240 Hertz, the collision-activated vibrational modes of carbon dioxide molecules do not have enough time to relax, or return to their original state. This came with an excellent benefit, as it turns out. The SuperCam microphone was included to record acoustic pressure fluctuations from the rover's laser-induced breakdown spectroscopy instrument as it ablates rock and soil samples at the Martian surface. Fortunately, Perseverance has something unique: microphones that can allow us to hear the sounds of Mars, and a laser that can trigger a perfectly timed noise. That alone means that sound would propagate differently on the red planet.īut the layer of the atmosphere just above the surface, known as the Planetary Boundary Layer, has added complications: During the day, the warming of the surface generates convective updrafts that create strong turbulence.Ĭonventional instruments for testing surface thermal gradients are highly accurate, but can suffer from various interference effects. Mars' atmosphere is a lot more tenuous than Earth's, around 0.020 kg/m 3, compared to about 1.2 kg/m 3 for Earth.