Astronomy

Back in 2007, I talked with Rob Manning, engineer extraordinaire at the Jet Propulsion Laboratory, and he told me something shocking. Even though he had successfully led the entry, descent, and landing (EDL) teams for three Mars rover missions, he said the prospect of landing a human mission on the Red Planet might be impossible.

But now, after nearly 20 years of work and research — as well as more successful Mars rover landings — Manning says the outlook has vastly improved.

“We’ve made huge progress since 2007,” Manning told me when we chatted a few weeks ago in 2024. “It’s interesting how its evolved, but the fundamental challenges we had in 2007 haven’t gone away, they’ve just morphed.”

Image of the Martian atmosphere and surface obtained by the Viking 1 orbiter in June 1976. (Credit: NASA/Viking 1)

The problems arise from the combination of Mars’ ultra-thin atmosphere—which is over 100 times thinner than Earth’s — and the ultra-large size of spacecraft needed for human missions, likely between 20 – 100 metric tons.

“Many people immediately conclude that landing humans on Mars should be easy,” Manning said back in 2007, “since we’ve landed successfully on the Moon and we routinely land human-carrying vehicles from space to Earth. And since Mars falls between the Earth and the Moon in size and in the amount of atmosphere, then the middle ground of Mars should be easy.”

But Mars’ atmosphere provides challenges not found on Earth or the Moon. A large, heavy spacecraft  streaking through Mars’ thin, volatile atmosphere only has just a few minutes to slow from incoming interplanetary speeds (for example, the Perseverance rover was traveling 12,100 mph [19,500 kph] when it reached Mars) to under Mach 1, and then quickly transition to a lander to slow to be able to touch down gently.

Universe Today publisher Fraser Cain’s video about the challenges of landing Mars, with more details in this article.

In 2007, the prevailing notion among EDL engineers was that there’s too little atmosphere to land like we do on Earth, but there is actually too much atmosphere on Mars to land heavy vehicles like we do on the Moon by using propulsive technology alone.

“We call it the Supersonic Transition Problem,” said Manning, again in 2007. “Unique to Mars, there is a velocity-altitude gap below Mach 5. The gap is between the delivery capability of large entry systems at Mars and the capability of super-and sub-sonic decelerator technologies to get below the speed of sound.”

The largest payload to land on Mars so far is the Perseverance rover, which has a mass of about 1 metric ton. Successfully landing Perseverance and its predecessor Curiosity required a complicated, Rube Goldberg-like series of maneuvers and devices such as the Sky Crane. Larger, human-rated vehicles will be coming in even faster and heavier, making them incredibly difficult to slow down.

Rob Manning, Chief Engineer for NASA’s Jet Propulsion Laboratory, and the Sky Crane for landing rovers on Mars. Credit: NASA/JPL-Caltech/Keck Institute

“So, how do you slow down to subsonic speeds,” Manning said now in 2024 as the chief engineer at JPL, “to get to speeds where traditionally we know how to fire our engines to enable touchdown? We thought bigger parachutes or supersonic decelerators like LOFTID (Low-Earth Orbit Flight Test of an Inflatable Decelerator) tested by NASA) would allow us to maybe slow down better, but there were still issues with both those devices.”

“But there was one trick we didn’t know anything about it,” Manning continued. “How about using your propulsion system and firing the engines backwards —retro propulsion — while you are flying at supersonic speeds to shed velocity? Back in 2007, we didn’t know the answer to that. We didn’t even think it was possible.”

Why not? What could go wrong?

“When you fire engines backwards as you are moving through an atmosphere, there’s a shock front that forms and it would be moving around,” Manning explained, “so it could come along and whack the vehicle and cause it to go unstable or cause damage. You’re also flying right into the plume of the rocket engine exhaust, so there could be extra friction and heating possibilities on the vehicle.”

All of this is very hard to model and there was virtually no experience doing it, as in 2007, no one had ever used propulsive technology alone to slow and then land a spacecraft back on Earth. This is mostly because our planet’s beautiful, luxuriously thick atmosphere slows a spacecraft down easily, especially with a parachute or creative flying as the space shuttle did.

“People did study it a bit, and we came to the conclusion it would be great to try it and find out whether we could fire engines backwards and see what happens,” Manning mused, adding that there wasn’t any extra funding laying around to launch a rocket just to watch it come down again to see what happened.

A SpaceX Falcon-9 rocket poised to launch Dragon from Cape Canaveral. Credit: NASA

But then, SpaceX started doing tests in attempt to land their Falcon 9’s first stage booster back on Earth to re-use them.

“SpaceX said they were going to try it,” Manning said, “And to do that they needed to slow the booster down in the supersonic phase while in Earth’s upper atmosphere. So, there’s a portion of the flight where they fire their engines backwards at supersonic speeds through a rarified atmosphere which is very much what’s like at Mars.”

As you can imagine, this was incredibly intriguing to EDL engineers thinking about future Mars missions.

After a few years of trial, error, and failures, on September 29, 2013, SpaceX performed the first supersonic retropropulsion (SRP) maneuver to decelerate the reentry of the first stage of their Falcon 9 rocket. While it ultimately hit the ocean and was destroyed, the SRP actually worked to slow down the booster.

NASA asked if their EDL engineers could watch and study SpaceX’s data, and SpaceX readily agreed. Beginning in 2014, NASA and SpaceX formed a three-year public-private partnership centered on SRP data analysis called the NASA Propulsive Descent Technology (PDT) project.  The F9 boosters were outfitted with special instruments to collect data specifically on portions of the entry burn which fell within the range of Mach numbers and dynamic pressures expected at Mars. Additionally, there were visual and infrared imagery campaigns, flight reconstruction, and fluid dynamics analysis – all of which helped both NASA and SpaceX.

To everyone’s surprise and delight, it worked. On December 21, 2015, an F9 first stage returned and successfully landed on Landing Zone 1 at Cape Canaveral, the first-ever orbital class rocket landing. This was a game changing demonstration of SRP, which advanced the knowledge and tested the technology of using SRP on Mars.

View of SpaceX Falcon 9 first stage approaching Landing Zone 1 on Dec. 21, 2015. Credit: SpaceX

“Based on the analyses completed, the remaining SRP challenge is characterized as one of prudent flight systems engineering dependent on maturation of specific Mars flight systems, not technology advancement,” wrote an EDL team, detailing the results of the PDT project in a paper. In short, SpaceX’s success meant it wouldn’t require any fancy new technology or breaking the laws of physics to land large payloads on Mars.

“It turns out, we learned some new physics,” Manning said. They found that the shock front ‘bubble’ created around the vehicle by firing the engines somehow insulates the spacecraft from any buffeting, as well as from some of the heating.

EDL engineers now believe that SRP is the only Mars entry, descent and landing technology that is intrinsically scalable across a wide range and size of missions to shed enough velocity during atmospheric flight to enable safe landings. Alongside aerobraking, this is one of the leading means of landing heavy equipment, habitats and even humans on Mars.

But still, numerous issues remain unsolved when it comes to landing a human mission on Mars. Manning mentioned there are multiple unknowns, including how a big ship such as SpaceX’s Starship would be steered and flown through Mars’ atmosphere; can fins be used hypersonically or will the plasma thermal environment melt them? The amount of debris kicked up by large engines on human-sized ship could be fatal, especially for the engines you’d like to reuse for returning to orbit or to Earth, so how do you protect the engines and the ship? Mars can be quite windy, so what happens if you encounter wind shears or a dust storm during landing? What kind of landing legs will work for a large ship on Mars’ rocky surface? Then there are logistics problems such as how will all the infrastructure get established? How will ships be refueled to return home?

“This is all going to take a lot of time, more time than people realize,” Manning said. “One of the downsides of going to Mars is that it is hard to do trial and error unless you are very patient. The next time you can try again is 26 months later because of the timing of the launch windows between our two planets. Holy buckets, what a pain that is going to be! But I think we’re going to learn a lot whenever we can try it for the first time.”

And at least the supersonic retropropulsion question has been answered.

“We’re basically doing what Buck Rogers told us to do back in the 1930s: fire your engines backwards while you’re going really fast.”

2007 article: The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet

The post The New Mars Landing Approach: How We’ll Land Large Payloads on the Red Planet appeared first on Universe Today.

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One of the surprise findings with the James Webb Space Telescope is the discovery of massive galaxies in the early Universe. The expectations were that only young, small, baby galaxies would exist within the first billion years after the Big Bang. But some of the newly found galaxies appear to be as large and as mature as galaxies that we see today.  

Three more of these “monster” galaxies have now been found, and they have a similar mass to our own Milky Way. These galaxies are forming stars nearly twice as efficiently as galaxies that were formed later on in the Universe. Although they’re still within standard theories of cosmology, researchers say they demonstrate how much needs to be learned about the early Universe.

‘‘Our findings are reshaping our understanding of galaxy formation in the early Universe,’’ said Dr. Mengyuan Xiao, lead author of the new study and postdoctoral researcher at the University of Geneva, in a press release.

The most widely accepted cosmological model is the Lambda Cold Dark Matter (LCDM) model which posits that the first galaxies in the Universe did not have enough time to become so massive and should have been more modestly sized.

The new findings, published in the journal Nature, were made using JWST’s spectroscopic capabilities at near-infrared wavelengths. This allows astronomers to systematically study galaxies in the very distant and early Universe, including these three massive and dust-obscured galaxies. The study was conducted as part of the telescope’s FRESCO program (First Reionization Epoch Spectroscopically Complete Observations), which uses JWST’s NIRCam/grism spectrograph to measure accurate distances and stellar masses of galaxies. The results may indicate that the formation of stars in the early Universe was far more efficient than previously thought, which does challenge existing galaxy formation models.

The JWST NIRCAM operates over a wavelength range of 0.6 to 5 microns. Credit: NASA.

However, there has been some controversy as to whether these galaxies really are super-large and mature. In August, another study debated the earlier findings of “impossibly large” galaxies, saying that what was observed may have been the result of an optical illusion, as the presence of black holes in some of these early galaxies made them appear much brighter and larger than they actually were.

But this latest study was part of the new FRESCO program with JWST to systematically analyze a complete sample of galaxies within the first billion years of cosmic history to determine whether they are dominated by ionization from young stars (starburst galaxies) or by an active galactic nucleus (AGN), i.e., a black hole. The researchers say this new approach allows for precise distance estimates and reliable stellar mass measurements for the full galaxy sample.

‘‘Our findings highlight the remarkable power of NIRCam/grism spectroscopy,” said Pascal Oesch, also from the University of Geneva, and principal investigator of the FRESCO program. ‘‘The instrument on board the space telescope allows us to identify and study the growth of galaxies over time, and to obtain a clearer picture of how stellar mass accumulates over the course of cosmic history.’’

Images of six candidate massive galaxies, that were reported in February 2023, seen 500-700 million years after the Big Bang. One of the sources (bottom left) could contain as many stars as our present-day Milky Way, according to researchers, but it is 30 times more compact. Credit: NASA, ESA, CSA, I. Labbe (Swinburne University of Technology). Image processing: G. Brammer (Niels Bohr Institute’s Cosmic Dawn Center at the University of Copenhagen).

Researchers will certainly be making further observations of all these newly seen galaxies, which hopefully will help resolve any remaining questions about how massive these galaxies are and whether or not star formation was more rapid during the early Universe. The new observations of more of the large but young galaxies raises the question of whether the galaxies really are surprising monsters or optical illusions. Either way, all the findings raise new questions about the formation process of stars and galaxies in the early Universe.

“There is still that sense of intrigue,” said Katherine Chworowsky, a graduate student at the University of Texas at Austin (UT), who led the study we reported on in August. “Not everything is fully understood. That’s what makes doing this kind of science fun, because it’d be a terribly boring field if one paper figured everything out, or there were no more questions to answer.”

Further reading:

University of Geneva
UC Santa Cruz
Nature

The post Three More “Galactic Monster” Ultra-Massive Galaxies Found appeared first on Universe Today.

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We have been spoiled over recent years with first the Hubble Space Telescope (HST) and then the James Webb Space Telescope (JWST.) Both have opened our eyes on the Universe and made amazing discoveries. One subject that has received attention from both is the derivation of the Hubble Constant – a constant relating the velocity of remote galaxies and their distances. A recent paper announces that JWST has just validated the results of previous studies by the Hubble Space Telescope to accurately measure its value. 

The Hubble Constant (H0) is a fundamental parameter in cosmology that defines the rate of expansion of the universe. It defines the relationship between Earth and distant galaxies by the velocity they are receding from us. It was first discussed by Edwin Hubble in 1929 as he observed the spectra of distant galaxies. It is measured in unites of kilometres per second per megaparsec and shows how fast galaxies are moving away from us per unit of distance. The exact value of the constant has been the cause of many a scientific debate and more recently the HST and JWST have been trying to fine tune its value. Getting an accurate value is key to determining the age, size and fate of the universe. 

Edwin Hubble

A paper recently published by a team of researchers led by Adam G. Riess from John Hopkins University validate the results from a previous HST study. They use JWST to explore its earlier results of the cepheid/supernova distance ladder. This has been used to establish distances across the cosmos using cepheid variable stars and Type 1a supernovae. Both objects can be likened to ‘standard candles’ whose actual brightness is very well understood. By measuring their apparent brightness from Earth, their distances can be calculated by comparing it to their actual brightness, their intrinsic luminosity.

NASA’s James Webb Space Telescope has spotted a multiply-imaged supernova in a distant galaxy designated MRG-M0138. Image Credit: NASA, ESA, CSA, STScI, Justin Pierel (STScI) and Andrew Newman (Carnegie Institution for Science).

Over recent decades, a number of attempts have been made to accurately determine H0 using a multitude of different instruments and observations. The cosmic microwave background has been used along with the aforementioned studies using cepheid variables and supernovae events. The results provide a range of results which has become known as ‘Hubble tension.’ The recent study using JWST hopes that it may be able to fine tune and validate previous work. 

To be able to determine H0 with a level of accuracy using the cepheid/supernova ladder, a sufficiently high sample of cepheids and supernovae must be observed. This has been challenging, in particular of the sample size of supernovae within the range of cepheid variable stars. The team also explored other techniques for determining H0 for example studying data from HST of the study of the luminosity of the brightest red giant branch stars in a galaxy – which can also work as a standard candle. Or the luminosity of certain carbon rich stars which are another technique. 

This illustration shows three steps astronomers used to measure the universe’s expansion rate (Hubble constant) to an unprecedented accuracy, reducing the total uncertainty to 2.3 percent. The measurements streamline and strengthen the construction of the cosmic distance ladder, which is used to measure accurate distances to galaxies near to and far from Earth. The latest Hubble study extends the number of Cepheid variable stars analyzed to distances of up to 10 times farther across our galaxy than previous Hubble results. Credits: NASA, ESA, A. Feild (STScI), and A. Riess (STScI/JHU)

The team conclude that, when all JWST measurements are combined, including a correction for the low sample of supernovae data, that H0 comes out at 72.6 ± 2.0 km s?1 Mpc?1  This compares to the combined HST data which determines H0 as 72.8 km s?1 Mpc?1  It will take more years and more studies for the sample size of supernova from JWST to equal that from HST but the cross-check has so far revealed we are finally honing in on an accurate value for Hubble’s Constant.

Source : JWST Validates HST Distance Measurements: Selection of Supernova Subsample Explains Differences in JWST Estimates of Local H0

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