The Times Australia
The Times World News

.
The Times Real Estate

.

The BOLT II hypersonic flight test could bring superfast global travel a step closer

  • Written by Chris James, ARC DECRA Fellow, Centre for Hypersonics, School of Mechanical and Mining Engineering, The University of Queensland
The BOLT II hypersonic flight test could bring superfast global travel a step closer

The BOLT II hypersonic flight experiment will launch tonight from NASA’s Wallops Test Flight Facility[1] in Virginia.

Hypersonic vehicles, which can fly much faster than passenger jets, would allow passengers to go from Sydney to Los Angeles, for instance, in just a couple of hours.

They could also offer more flexible options for launching payloads into space than conventional rockets and their speed and manoeuvrability mean they have a range of potential tactical military uses too.

Russia and China already claim to have operating hypersonic missiles[2], but hypersonic passenger aviation is still a dream rather than reality.

Read more: Hypersonic missiles are fuelling fears of a new superpower arms race[3]

Nevertheless, several types of hypersonic vehicles already exist, including rockets, planetary entry vehicles such as SpaceX’s Dragon capsule[4] and intercontinental ballistic missiles.

What is hypersonic flight?

Hypersonic flight is faster than supersonic flight – the latter term, by definition, means faster than the speed of sound.

To break the sound barrier – and surpass “Mach 1” – you need to travel faster than about 1,235km per hour, or a kilometre in just under 3 seconds. Mach 2 is twice as fast, and so on.

There is no clearly defined Mach number that marks the boundary between supersonic and hypersonic flight. But Mach 5[5] is generally taken by aerospace engineers to be where hypersonic speed begins.

Hypersonic travel presents a few extra problems that aren’t encountered at more pedestrian speeds. Chief among these is the fact that the air flow over the vehicle causes so much friction the outside of the craft can exceed 1,000℃.

Like all aircraft, flying depends on not having too much mass on board. So specialist materials, either high-temperature ceramics or “ablative” materials that slowly burn away during flight[6], are required on the outside of vehicles to insulate the craft against this heat and still be light enough to fly.

Hypersonic engines, called scramjets (supersonic combustion ramjets), need to burn fuel in a supersonic air flow, which is very complicated.

Artist’s impression of the Boeing X-51A Waverider, a scramjet powered hypersonic test vehicle. U.S. Air Force

Another persistent issue is that hypersonic flight is difficult to model accurately, because of the interplay of various different physical effects that come into play at extreme speeds.

So if you want to understand everything together, you have to do real flight tests such as today’s launch. But these are expensive and technically demanding.

Read more: The race to hypersonic speed: will air passengers feel the benefits?[7]

Testing boundaries

One of the trickiest hypersonic problems is predicting something called the “boundary layer transition location”.

When an aircraft flies through the air, a thin layer of air forms around its surface and is dragged along with the vehicle.

This “boundary layer” is very important, as most of the heating happens here, along with a significant portion of the drag forces that try to slow down the vehicle.

As this boundary layer grows along the vehicle’s length, it will eventually “transition” from the calm “laminar” flow near the leading edge of the vehicle, to violent “turbulent” flow further downstream.

Gas flow transitioning from laminar, transitional (in between) and then turbulent on a flat plate. David L. Chandler, MIT News Office

While we understand what leads to this “boundary layer transition”, we can’t perfectly predict it, especially at hypersonic speeds.

The problem is that predicting the boundary layer transition location accurately is very important for designing hypersonic vehicles. In most cases, turbulent flow is bad. It greatly increases both heating and drag.

Uncertainty in where the flow will be turbulent is a major issue, as large heating and drag uncertainties make some vehicle designs inefficient or completely unfeasible.

BOLT II: a new transition flight experiment

BOLT (short for Boundary Layer Transition) was a US$6 million[8] hypersonic flight test that launched in June 2021 from Esrange Space Center in northern Sweden to study boundary layer transition.

But it failed to reach hypersonic speeds, after problems with its rocket launch mechanism.

BOLT II (this time short for Boundary Layer Transition and Turbulence) is the next planned flight in the program, with a similar budget but a larger vehicle to ensure more flow turbulence can be studied[9].

Both the BOLT and BOLT II vehicles have a complex, swept geometry with a concave surface to represent a real hypersonic vehicle[10]. The aim is to produce complex, real-world data that engineers and scientists can use to improve their models for predicting transition on hypersonic vehicles.

A separate experiment is run on each side of the vehicle, with one “smooth” side and one “rough” side[11]. The flow running length along the vehicle is 1 metre[12], slightly larger than the original BOLT vehicle.

BOLT II will be launched on a suborbital trajectory by a two-stage sounding rocket[13]. During its ascent, it is planned to reach Mach 6, where an ascent flight experiment will occur[14]. It will turn over in space and then re-enter the atmosphere, before performing a descent experiment at Mach 5.5[15].

BOLT II is a fully autonomous vehicle and it has more than 400 sensors and instruments mounted onboard[16] to capture data about the flow environment during the experiments.

Assuming that BOLT II’s planned trajectory will be similar to the planned original BOLT flight trajectory, BOLT II will reach a maximum altitude of around 281km[17]. The whole mission will be over in less than 10 minutes after launch[18].

The original BOLT flight vehicle before testing. Air Force Office of Scientific Research/Johns Hopkins APL

Where to from here?

To develop the hypersonic vehicles of the future, we need to properly understand how to predict boundary layer transition on realistic vehicle shapes and what the minute effects of turbulent flow on hypersonic vehicles are. Data from the BOLT II flight experiment will help do just that.

Read more: Sydney to London in an hour? The future of hypersonic air travel[19]

The launch will be livestreamed on the NASA Wallops Youtube channel[20], so we’ll know straight away if the flight is a success or not. Assuming it is, in the coming years we will see many scientific papers published on the breakthroughs from this significant experiment.

The ability to accurately predict hypersonic boundary layer transmission will bring us much closer to hypersonic passenger flight one day. NASA’s planned NASP hypersonic space-plane was cancelled in the 1990s, partly due to the inability to accurately predict its transition location[21]. Hopefully, soon we can move past that.

However, many issues will still remain. Air-breathing hypersonic engines are still in their infancy; the materials used to shield hypersonic vehicles are very expensive; and the design of hypersonic vehicles is still very complicated. Companies like Australia’s own Hypersonix, which aims to use an air-breathing hypersonic vehicle to launch small payloads into orbit[22], will hopefully bring us closer to making the hypersonic flight dream a reality.

References

  1. ^ tonight from NASA’s Wallops Test Flight Facility (www.afrl.af.mil)
  2. ^ operating hypersonic missiles (theconversation.com)
  3. ^ Hypersonic missiles are fuelling fears of a new superpower arms race (theconversation.com)
  4. ^ Dragon capsule (www.spacex.com)
  5. ^ Mach 5 (www.grc.nasa.gov)
  6. ^ either high-temperature ceramics or “ablative” materials that slowly burn away during flight (www.af.mil)
  7. ^ The race to hypersonic speed: will air passengers feel the benefits? (theconversation.com)
  8. ^ US$6 million (aerospaceamerica.aiaa.org)
  9. ^ larger vehicle to ensure more flow turbulence can be studied (aerospaceamerica.aiaa.org)
  10. ^ complex, swept geometry with a concave surface to represent a real hypersonic vehicle (arc.aiaa.org)
  11. ^ one “smooth” side and one “rough” side (arc.aiaa.org)
  12. ^ 1 metre (arc.aiaa.org)
  13. ^ two-stage sounding rocket (www.afrl.af.mil)
  14. ^ Mach 6, where an ascent flight experiment will occur (arc.aiaa.org)
  15. ^ descent experiment at Mach 5.5 (arc.aiaa.org)
  16. ^ more than 400 sensors and instruments mounted onboard (www.afrl.af.mil)
  17. ^ maximum altitude of around 281km (doi.org)
  18. ^ less than 10 minutes after launch (doi.org)
  19. ^ Sydney to London in an hour? The future of hypersonic air travel (theconversation.com)
  20. ^ NASA Wallops Youtube channel (www.youtube.com)
  21. ^ accurately predict its transition location (arc.aiaa.org)
  22. ^ air-breathing hypersonic vehicle to launch small payloads into orbit (hypersonix.com.au)

Read more https://theconversation.com/the-bolt-ii-hypersonic-flight-test-could-bring-superfast-global-travel-a-step-closer-179556

The Times Features

Best Deals on Home Furniture Online

Key Highlights Discover the best deals on high-quality outdoor furniture online. Transform your outdoor space into a stylish and comfortable oasis. Explore a wide range of d...

Discover the Best Women's Jumpers for Every Season

Key Highlights Explore lightweight jumpers for spring and summer, ensuring breathability and ease. Wrap up warm with cozy wool jumpers for the chilly autumn and winter season...

Uncover the Elegance of Gorgeous Diamond Tennis Necklaces

Key Highlights Diamond tennis necklaces are a timeless piece of jewelry that exudes elegance and sophistication. They feature a continuous line of brilliant-cut diamonds, cre...

Dental Implants vs. Dentures: Which Is Better for You?

When it comes to replacing missing teeth, two of the most common options are dental implants and dentures. Both have their advantages and disadvantages, so choosing between them ...

What Neck Pain Really Means (And Why It’s More Than Just Poor Posture)

Neck pain is often brushed off as something temporary — a tight spot after a long day at the desk or a poor night’s sleep. But when the discomfort keeps returning, it could be a ...

The Work of Gosha Rubchinskiy: Fashion, Culture, and Youth

From Designer to Cultural Architect Gosha Rubchinskiy is not just a fashion designer—he's a cultural force. Born in Moscow in 1984, Rubchinskiy began his career in fashion in t...

Times Magazine

The Essential Guide to Transforming Office Spaces for Maximum Efficiency

Why Office Fitouts MatterA well-designed office can make all the difference in productivity, employee satisfaction, and client impressions. Businesses of all sizes are investing in updated office spaces to create environments that foster collaborat...

The A/B Testing Revolution: How AI Optimized Landing Pages Without Human Input

A/B testing was always integral to the web-based marketing world. Was there a button that converted better? Marketing could pit one against the other and see which option worked better. This was always through human observation, and over time, as d...

Using Countdown Timers in Email: Do They Really Increase Conversions?

In a world that's always on, where marketers are attempting to entice a subscriber and get them to convert on the same screen with one email, the power of urgency is sometimes the essential element needed. One of the most popular ways to create urg...

Types of Software Consultants

In today's technology-driven world, businesses often seek the expertise of software consultants to navigate complex software needs. There are several types of software consultants, including solution architects, project managers, and user experienc...

CWU Assistive Tech Hub is Changing Lives: Win a Free Rollator Walker This Easter!

🌟 Mobility. Independence. Community. All in One. This Easter, the CWU Assistive Tech Hub is pleased to support the Banyule community by giving away a rollator walker. The giveaway will take place during the Macleod Village Easter Egg Hunt & Ma...

"Eternal Nurture" by Cara Barilla: A Timeless Collection of Wisdom and Healing

Renowned Sydney-born author and educator Cara Barilla has released her latest book, Eternal Nurture, a profound collection of inspirational quotes designed to support mindfulness, emotional healing, and personal growth. With a deep commitment to ...

LayBy Shopping