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Interview Part 2
On July 30, 2021 Tim Dodd received a tour of Starbase with SpaceX CEO, CTO, and founder Elon Musk. This article includes key takeaways from the first hour and 50 minutes of the over 2-hour-long interview.
Manufacturing:
Musk once again emphasized that manufacturing is underrated and design is overrated; developing a production system is 10-100 times harder than designing the product, which according to Musk, proved especially true with Raptor. Furthermore, as volume production increases the amount of effort that goes into design rounds down to 0.
For example, Musk stated that designing a closed-cycle engine is easy. However, the extremely hard part is getting the cost-per-tonne of thrust under $1,000 – with each Raptor producing 230 tonnes of thrust, this means that each engine must cost less than $230,000 to produce. Musk continued stating that the cost-per-tonne to orbit, and the cost-per-tonne to the surface of Mars, is several orders of magnitude too high on current launch vehicles. For this reason, it is so important to move as much mass and complexity as possible to the ground systems, which Musk is calling “stage 0.” For example, SpaceX has opted to not fuel Starship through the booster, and will rather move the complexity and mass to the ground and fuel Starship from its side.
Super Heavy Design:
Musk noted that Super Heavy’s dry mass should be under 200 tonnes, although the dry mass is a moving target. The engines, including mounting mass, are 2 tonnes; the fuel tank and the liquid oxygen (LOx) tanks are roughly 80 tonnes; and the interstage is around 20 tonnes, including four grid fins that each weigh roughly 3 tonnes. Musk noted that he expects to be able to cut the mass of each grid fin in half, and that the current design is very mass inefficient. He further noted that currently everything is too heavy, including avionics, grid fins, and batteries.
The grid fins are currently electrically powered, using a modified Tesla Model 3 motor to drive them. In continuation of using Tesla parts, the batteries are currently energy optimized instead of power optimized, as a car needs several hours of energy, whereas the grid fins only need two or three minutes of power. Due to these reasons, Musk noted, like much of Starship’s design, the batteries are temporary, and battery mass can drop by a factor of ~10.
The booster is designed to carry 3,600 tonnes of propellant, of which ~78% of that is liquid oxygen. The Raptor burns at a mixture ratio of 3.5 to 3.7, which is fuel rich. A fuel rich mixture burns cooler than the stoichiometric ratio, which would melt the engine. Super Heavy’s propellant residuals (the amount of fuel that cannot be used without risking damage to the vehicle) are on the order of 20 tonnes, Musk notes, which is significantly higher than the 1 tonne propellant residual of the Falcon 9. With optimizations to design Musk noted that the final dry mass of Super Heavy should be between 160 and 200 tonnes.
An interesting note is the grid fins on Super Heavy do not fold in like on the Falcon 9, as they are another mechanism, which adds unnecessary complexity, mass, and failure modes. Additionally, the increase in drag from the grid fins being deployed during ascent is small, assuming they are not at a high angle of attack.
The grid fins on Super Heavy are not evenly spaced 90° apart, like on the Falcon 9. Musk said the reason for this change is Super Heavy requires more pitch control authority, so they positioned the gridfins closer together to increase pitch control.
面试第二部分
2021年7月30日，蒂姆·多德与SpaceX首席执行官、首席技术官兼创始人埃隆·马斯克一起参观了StarBase。这篇文章包括了长达2个多小时的采访的前1小时50分钟的主要内容。
制造业：
马斯克再次强调，制造被低估了，设计被高估了；开发生产系统比设计产品困难10-100倍，根据马斯克的说法，猛禽的情况尤其如此。此外，随着批量生产的增加，投入设计的工作量四舍五入为0。
例如，马斯克表示，设计闭合循环发动机很容易。然而，最困难的部分是将每吨推力的成本控制在1000美元以下--每架猛禽飞机产生230吨推力，这意味着每台发动机的生产成本必须低于23万美元。马斯克继续说，在目前的运载火箭上，轨道每吨的成本，以及火星表面的每吨成本，都高出了几个数量级。出于这个原因，将尽可能多的质量和复杂性转移到地面系统是非常重要的，马斯克将其称为“0阶段”。例如，SpaceX已经选择不通过助推器为星际飞船提供燃料，而是将复杂性和质量转移到地面，并从其一侧为星际飞船提供燃料。
超重设计：
马斯克指出，超重的干质量应该在200吨以下，尽管干质量是一个移动的目标。发动机(包括安装质量)为2吨；燃料箱和液氧(Lox)箱约为80吨；级间约为20吨，包括4个网格翅片，每个重约3吨。马斯克指出，他希望能够将每个栅格翅片的质量减半，目前的设计效率非常低。他进一步指出，目前所有东西都太重了，包括航空电子设备、栅格鳍和电池。
电网翅片目前是电力驱动的，使用改装的特斯拉Model3电机来驱动它们。在继续使用特斯拉部件的情况下，电池目前是能量优化的，而不是功率优化的，因为一辆汽车需要几个小时的能源，而电网翅片只需要两三分钟的电力。马斯克指出，由于这些原因，就像星际飞船的大部分设计一样，电池是临时的，电池质量可能会下降约10倍。
助推器设计运载3600吨推进剂，其中约78%是液氧。猛禽的燃烧混合比为3.5：3.7，燃料丰富。富含燃料的混合气燃烧的温度比化学计量比要低，这会使发动机熔化。马斯克指出，超重的推进剂残留量(不能在不对车辆造成损害的情况下使用的燃料量)约为20吨，远远高于猎鹰9号1吨的推进剂残留量。马斯克指出，经过优化设计，超重的最终干质量应该在160吨到200吨之间。
有趣的是，超级重型上的栅格鳍不会像猎鹰9号那样折叠起来，因为它们是另一种机制，增加了不必要的复杂性、质量和故障模式。此外，假设栅格尾翼没有处于大攻角，那么在上升过程中展开的栅格尾翼所增加的阻力是很小的。
与猎鹰9号不同，超重型的栅格鳍间距不是均匀的90°。马斯克说，这一变化的原因是超重型需要更多的俯仰控制权，所以他们将栅格鳍放置在更近的位置，以加强俯仰控制。
Musk’s Engineering Philosophy:
Musk overviewed his five step engineering process, which must be completed in order:
Make the requirements less dumb. The requirements are definitely dumb; it does not matter who gave them to you. He notes that it’s particularly dangerous if an intelligent person gives you the requirements, as you may not question the requirements enough. “Everyone’s wrong. No matter who you are, everyone is wrong some of the time.” He further notes that “all designs are wrong, it’s just a matter of how wrong.”
Try very hard to delete the part or process. If parts are not being added back into the design at least 10% of the time, not enough parts are being deleted. Musk noted that the bias tends to be very strongly toward “let’s add this part or process step in case we need it.” Additionally, each required part and process must come from a name, not a department, as a department cannot be asked why a requirement exists, but a person can.
Simplify and optimize the design. This is step three as the most common error of a smart engineer is to optimize something that should not exist.
Accelerate cycle time. Musk states “you’re moving too slowly, go faster! But don’t go faster until you’ve worked on the other three things first.”
Automate. An important part of this is to remove in-process testing after the problems have been diagnosed; if a product is reaching the end of a production line with a high acceptance rate, there is no need for in-process testing.
Additionally, Musk restated that he believes everyone should be a chief engineer. Engineers need to understand the system at a high level to understand when they are making a bad optimization. As an example, Musk noted that an order of magnitude more time has been spent reducing engine mass than reducing residual propellant, despite both being equally as important.
马斯克的工程哲学：
马斯克回顾了他的五个步骤的工程流程，这些流程必须完成，以便：
让需求变得不那么愚蠢。这些要求绝对是愚蠢的；是谁给你的并不重要。他指出，如果一个聪明人给你提出要求，那是特别危险的，因为你可能不会对这些要求提出足够的质疑。“每个人都错了。不管你是谁，每个人都有错的时候。“他进一步指出，“所有的设计都是错误的，这只是一个错误程度的问题。”
非常努力地删除部件或工艺。如果至少有10%的时间没有将部件添加回设计中，则说明没有删除足够的部件。马斯克指出，这种倾向倾向于非常强烈地倾向于“让我们添加这个部分或过程步骤，以防我们需要它。”此外，每个必需的部件和流程必须来自名称，而不是部门，因为不能询问部门为什么存在需求，但人可以。
简化和优化设计。这是第三步，因为聪明工程师最常见的错误是优化不应该存在的东西。
加快循环时间。马斯克说：“你走得太慢了，快点！但在你先做完其他三件事之前，不要走得更快。“
自动化。其中一个重要的部分是在诊断出问题后删除过程中的测试；如果产品在高合格率的生产线上接近尾声，则不需要过程中的测试。
此外，马斯克重申，他认为每个人都应该成为总工程师。工程师需要在高层次上了解系统，以了解他们何时进行了糟糕的优化。例如，马斯克指出，减少发动机质量所花的时间比减少残留推进剂的时间多出一个数量级，尽管两者同等重要。
Raptor:
Musk noted that SpaceX has produced parts of version 2 of Raptor, called Raptor 2, including the thrust chamber assembly. Teams have finished the design of the turbo pumps, and are expecting to be ready to fire the first Raptor 2 by the end of August. Raptor 2 will reach 230 tonnes of thrust at 298 bar main combustion chamber pressure, with Musk commenting “come on… we have to get 2 more bar out of that thing!” Raptor 2 features a larger throat, which decreases the area ratio; this causes a decrease in specific impulse of around 3 seconds, but increases thrust significantly. Despite having a lower ISP, this allows for booster engines to be more efficient as it decreases gravity losses. Musk noted that Raptor 2 will be significantly cleaner looking than Raptor 1, as they will remove a large amount of plumbing.
Raptor Vacuum has a brazed steel tube wall nozzle extension that has an expansion ratio of around 80, giving the engine a specific impulse (ISP) of 378 seconds. Musk noted that teams are hoping to get the expansion ratio up to 90, which would increase the ISP to 380 seconds. Long term, SpaceX will have three Raptor variants: sea level engine with gimbal, sea level engine without gimbal, and vacuum level engine without gimbal.
It was also stated that SpaceX will move volume production of Raptor to McGregor, but keep the Hawthorne factory for development engines and Raptor Vacuum versions.
Starship Separation System and Attitude Control:
Following Musk’s five step plan, SpaceX has decided to remove the pushing separation system from Starship and will instead rely on conservation of angular momentum to separate the stages. Right before main engine cutoff (MECO), Super Heavy will gimbal its engines, causing the vehicle to start rotating. The latches between Starship and Super Heavy will then release, causing the vehicles to float apart; the whole process is similar to how SpaceX deploys the Starlink satellites. This serves two purposes, as it separates the stages while starting the booster’s flip, which it needs to conduct for the boost back burn.
In addition to this, SpaceX has decided to remove the dedicated hot gas thrusters from Super Heavy. To replace it, SpaceX will use the ullage gas from the tanks for attitude control by having four vents spaced 90° apart. By venting the tanks through these vents, they will be able to control the attitude of the booster during the flip. This has the advantage of using the ullage gas, which would need to be vented either way, to do useful work to the vehicle.
HLS:
Once again following Musk’s five step process, Musk outlined that he is optimistic that HLS will not need the landing thrusters at the top of the lunar Starship. If SpaceX is able to demonstrate that landing on the moon with Raptor will not create too large of a hole in the lunar regolith, they may remove the thrusters from the lunar Starship. While the exact Raptor configuration for lunar Starship has not been decided, it is likely that it’ll be the same as the Earth variant with three sea-level Raptors and three vacuum Raptors.
Starship Design Philosophy:
Musk noted that SpaceX has polar opposite design methods for Starship and Dragon. He continued, saying that Dragon can never fail, must be tested extreme amounts, and has tons of margin. However, to develop the world’s first fully and rapidly reusable rocket SpaceX must iterate rapidly, which leads to lots of failures. Falcon is in-between, where SpaceX can afford to have a landing failure, but cannot experience a failure during ascent. In response to Dodd asking what SpaceX learned from the Space Shuttle, Musk continued stating that the biggest problem with the shuttle was that its design froze. Due to all Space Shuttle missions being crewed, design changes were high risk and low reward. Musk contrasts, stating the biggest advantage of Starship is “Starship does not have anyone on board so we can blow things up. It’s really helpful.”
In response to this, Dodd asked if Starship will ever have a launch escape system (LES). Musk explained that there are no plans to add LES and that instead Starship will fly a lot and have enough redundancy. Super Heavy will be able to lose several engines during ascent, while still having a fully successful mission, and an engine on Starship. Additionally, Musk stated that due to the inability to have an escape system on the moon and Mars, there is no reason to have one at all.
Furthermore, Musk noted that SpaceX’s goal is to push the envelope with each vehicle, such that it blows up, as this ensures SpaceX is getting lots of data while not having to store many vehicles. He further noted that every Starship has had major upgrades over the previous vehicle; such is the pace at Starbase. Because of this, the first 10 Starship’s that SpaceX gets back will likely not be reflown, as newer vehicles will be so vastly different.
猛禽：
马斯克指出，SpaceX已经生产了名为猛禽2的第二版猛禽的部件，包括推力室组件。团队已经完成了涡轮增压泵的设计，并预计在8月底之前准备发射第一架猛禽2号。猛禽2号将在298bar主燃烧室压力下达到230吨的推力，马斯克评论道：“加油…我们得从那玩意儿里再弄出两根铁棒！“猛禽2的特点是喉部更大，这会降低面积比；这会导致比冲降低约3秒，但推力会显著增加。尽管ISP较低，但这使得助推器引擎效率更高，因为它减少了重力损失。马斯克指出，猛禽2号的外观将比猛禽1号干净得多，因为它们将移除大量的管道。
猛禽真空有一个钎焊钢管壁喷嘴延伸部，膨胀比约为80，使发动机的比冲(ISP)为378秒。马斯克指出，团队希望将扩容比率提高到90%，这将使ISP增加到380秒。从长远来看，SpaceX将有三种猛禽发动机：有万向节的海平面发动机，没有万向节的海平面发动机和没有万向节的真空水平发动机。
还表示，SpaceX将把猛禽的批量生产转移到麦格雷戈，但保留霍桑工厂，生产开发发动机和猛禽真空版本。
星际飞船分离系统和姿态控制：
根据马斯克的五步计划，SpaceX公司决定从星际飞船上移除推力分离系统，转而依靠角动量守恒来分离级。就在主引擎关闭(MECO)之前，超重型将使发动机万向节，导致车辆开始旋转。“星际飞船”和“超级重型”之间的插销随后会松开，导致两个飞行器漂浮分开；整个过程类似于SpaceX部署Starlink卫星的过程。这有两个目的，因为它在启动助推器翻转的同时将两个阶段分开，这需要进行助推器的背部燃烧。
除此之外，SpaceX已经决定从超重型中移除专用的热气推进器。取而代之的是，SpaceX将使用水箱中的空隙气体进行姿态控制，将四个通风口间隔90°。通过这些通风口排出油箱，他们将能够控制助推器在翻转过程中的姿态。这样做的好处是，无论哪种方式，都需要使用需要排气的空隙气体来对车辆进行有用的工作。(工业和信息化部电子科学技术情报研究所陈皓)
HLS：
根据马斯克的五个步骤，马斯克再次概述了他对HLS将不需要月球星际飞船顶部的着陆推进器的乐观态度。如果SpaceX公司能够证明，用猛禽登陆月球不会在月球表层造成太大的洞，他们可能会从月球星际飞船上移除推进器。虽然月球星际飞船的确切猛禽配置尚未确定，但它很可能与地球型号的三架海平面猛禽和三架真空猛禽相同。
星际飞船设计理念：
马斯克指出，SpaceX对星际飞船和龙有截然相反的设计方法。他继续说，龙永远不会失败，必须测试极端的金额，并且有大量的保证金。然而，要开发世界上第一个完全快速重复使用的火箭，SpaceX必须快速迭代，这导致了许多失败。猎鹰位于两者之间，SpaceX可以承受着陆失败，但不能在上升过程中经历失败。在回答多德询问SpaceX公司从航天飞机上学到了什么时，马斯克继续说，航天飞机最大的问题是它的设计冻结了。由于航天飞机的所有任务都是由机组人员完成的，设计更改风险很高，回报很低。马斯克则相反，他说“星际飞船”最大的优势是“星际飞船上没有任何人，所以我们可以炸毁一切。”这真的很有帮助。“
对此，多德询问星际飞船是否会有发射逃逸系统(LES)。马斯克解释说，目前还没有增加LES的计划，取而代之的是，星际飞船将大量飞行，并有足够的冗余。超重型在升空过程中会失去几个引擎，但仍然有一个完全成功的任务，星际飞船上还有一个引擎。此外，马斯克表示，由于无法在月球和火星上建立逃逸系统，因此根本没有理由建立一个。
此外，马斯克指出，SpaceX的目标是推动每一辆车的极限，这样它就会爆炸，因为这确保了SpaceX在不必存储太多车辆的情况下获得了大量数据。他进一步指出，每一艘星际飞船都比之前的运载火箭进行了重大升级；这就是星际基地的速度。正因为如此，SpaceX公司取回的前10艘星际飞船很可能不会被重装，因为新的飞行器将会有很大的不同。
TPS:
Dodd asked Musk how he was feeling about Starship’s Thermal Protection System (TPS), to which Musk responded “we’ll find out!” He added that the TPS tiles have been holding up well during the sub-orbital flight tests. Each tile is mechanically mounted in a way so that the tiles can move a small amount, ensuring they do not get damaged during the expanding and contracting of the tank and tiles during the temperature changes of fueling and reentry.
Starship’s TPS tiles are currently made in Florida at “the Bakery.” While not all of the tiles are uniform, SpaceX is able to mass produce the tiles due to them largely being the same shape and size, a significant advantage over the Space Shuttle’s TPS system. Additionally, Musk described the tiles as having “no meaningful limit” to their lifespan.
Musk stated that the hardest parts of the vehicle to protect against reentry heating are the flap hinges. Ensuring hot plasma does not get into the hinges and destroy the vehicle is not trivial, as the seal must simultaneously not damage the tiles and survive the heat of reentry; this means a metal seal is required.
With a full heatshield, S20’s dry mass will “hopefully not be much more than 100 tonnes.” Musk added that adding one tonne to the ship removes about two tonnes from the payload capacity, after taking into account the added mass and increase in propellant needed.
TPS：
多德问马斯克对“星际飞船”的热防护系统(TPS)有何感想，马斯克回答说：“我们会弄清楚的！”他补充说，TPS瓷砖在亚轨道飞行测试中表现良好。每一块瓷砖都是机械安装的，因此瓷砖可以少量移动，确保它们在油箱和瓷砖的扩张和收缩过程中不会受到损坏，在加油和再入温度变化期间也不会损坏。
星际飞船的TPS瓷砖目前在佛罗里达州的“面包房”(The Bakery)生产。虽然不是所有的瓷砖都是统一的，但SpaceX能够批量生产这些瓷砖，因为它们的形状和大小基本相同，这比航天飞机的TPS系统有显著的优势。此外，马斯克称瓷砖的使用寿命“没有任何意义上的限制”。
马斯克表示，飞行器最难防止再入热的部件是襟翼铰链。确保热等离子体不会进入铰链并摧毁车辆并不是一件微不足道的事，因为密封必须同时不损坏瓷砖并在再入热中幸存下来；这意味着需要金属密封。
有了完整的隔热罩，S20的干质量“希望不会超过100吨”。马斯克补充说，考虑到增加的质量和所需推进剂的增加，每增加一吨船将从有效载荷能力中移除约两吨。
Orbital Demonstration Flight:
Musk stated that on the orbital demonstration flight, S20 will reach orbital velocity, but have a positive perigee that is less than 80km. This will ensure the vehicle reenters safely in a controlled manner, even in the event of a failure. On the orbital flight, both the first stage (B4) and the second stage (S20) will be expended, as SpaceX’s goal for the first flight is to “make it to orbit without blowing up”. Additionally, SpaceX would like to demonstrate the ability to position the booster precisely, such that if the booster came down next to the tower, Mechazilla (the catching mechanism) would be able to catch it.
For the first orbital flight, SpaceX will use a crane to stack Starship on top of Super Heavy. While this is a harder way to stack the vehicles, it allows SpaceX to start testing the vehicle before the orbital launch tower is complete.
New Nosecone:
Musk noted that the new nosecone design consists of two rows of stretch formed steel, whereas the old nosecone was made from three sections of stamped sections. The new nosecone is made by stretching steel over a big tool, which creates a far smoother and cleaner final product. Musk also noted that SpaceX has stopped all work on the fairing door for now, as it is not needed for an orbital demonstration flight. In a similar manner, SpaceX has not started work on Starship in-orbit refueling, as it’s not needed in the short term.
轨道演示飞行：
马斯克表示，在轨道演示飞行中，S20将达到轨道速度，但近地点正值不到80公里。这将确保车辆在受控的方式下安全地重新进入，即使在发生故障的情况下也是如此。在轨道飞行方面，第一级(B4)和第二级(S20)都将扩大，因为SpaceX第一次飞行的目标是“在不爆炸的情况下进入轨道”。此外，SpaceX希望展示助推器精确定位的能力，这样如果助推器落在塔旁，Mechazilla(捕捉装置)就能抓住它。
对于第一次轨道飞行，SpaceX将使用起重机将星际飞船堆叠在超级重型的顶部。虽然这是一种更难堆叠运载火箭的方法，但它允许SpaceX在轨道发射塔完成之前开始测试运载火箭。
新的鼻锥：
马斯克指出，新的鼻锥体设计由两排拉伸成型的钢材组成，而旧的鼻锥体是由三段冲压部分制成的。新的鼻锥体是通过在一个大工具上拉伸钢材制成的，这样可以创造出更光滑、更清洁的最终产品。马斯克还指出，SpaceX目前已经停止了整流罩的所有工作，因为轨道演示飞行不需要整流罩。以类似的方式，SpaceX公司还没有开始星际飞船的在轨加油工作，因为短期内不需要这样做。
