ticoAg/ChineseCorpus-Kaggle-fanti huggingface dataset:
從Occam的消息傳遞范式已經演變出了一些派生語言，用來在和共享內存并行計算機之間遷移應用程序的時候，等夠達成一致的效能。第一個這種派生實例出現在耶魯大學于1990年設計的編程語言Ease之中。此后類似的模型陸續出現，松散的結合了SQL數據庫和面向對象語言比如Java，經常稱為模型，并廣泛的用于現在的大規模分布式系統中。隨著微處理器增加每芯片的處理器數目（多核），這個范式也出現在桌面計算機上。
演員模型可有效的描述為一類特殊化的面向進程系統，在其中消息傳遞模型被限制為一種簡單固定的情況，即每個進程（也就是演員）都有一個無限輸入隊列，任何其他進程都可以向它發送消息。
*  Sowders, Matthew, "ProcessJ: A process-oriented programming language" (2011). UNLV Theses, Dissertations, Professional Papers, and Capstones. Paper 1393.
《金之國水之國》是巖本奈緒創作的日本漫畫。描述與世無爭的A國公主與失業的B國工程師如何卷入兩國紛爭中心，並用智慧化解干戈。本作品2017年獲得《這本漫畫真厲害！》女性篇第1名及漫畫大賞第2名。
A國貿易興盛、富裕繁榮，被稱為金之國，B國資源充足，被稱為水之國，兩國相鄰，時常為了芝麻綠豆大的小事起衝突，最後終於為了清理狗大便的問題引起戰爭。神明介入仲裁，要A國最美的女子嫁到B國，B國最聰明的男子入贅A國。A國住在邊境的第93王女莎拉奉命與B國女婿成親，沒想到等到的竟是一隻小狗，為兩國和平，莎拉隱瞞鄰國沒送來聰明男子之事。而A國國王同樣也未派遣美女至B國，而是送了一隻小貓過去，B國奉命與美女成親的人是工程師納蘭巴耶爾，他也想方設法隱瞞沒有妻子的真相。一日莎拉的姊姊第一王女邀請莎拉及其夫婿參加茶會，煩惱的莎拉帶小狗盧庫曼在郊外散心，盧庫曼掉進洞穴裏，正巧經過的納蘭巴耶爾救出了小狗而與莎拉相識，莎拉請託納蘭巴耶爾假裝成她的丈夫應付第一王女之約，而兩國歷史的齒輪也開始轉動。
:A國第93王女，是國王住在邊陲側室的么女，性格溫婉，身材豐腴，因A國水資源稀少多以酒代水，酒量很好。奉命與B國男子成親卻迎來一隻小狗，為兩國和平對外隱瞞此事，將小狗取名為盧庫曼。
;納蘭巴耶爾
:B國一圖書館長之子，原為工程師，但因兩國爆發戰爭致工程停擺失業中，奉命迎娶A國女子卻等到一隻小貓，與父親對外隱瞞此事，將小貓取名為奧東齊梅格。知道A國缺水情況後，找左大臣合作在A國建造水路引水。
;拉斯塔邦三世
:A國國王，與900年前跟B國和平共處的拉斯塔邦二世同名，因在現代二世被說成是不敢得罪B國的膽小王，對此耿耿於懷。為羞辱B國沒依約讓女子和親反而送去一隻小貓。
;蕾歐波爾提涅
:A國第一王女，是務實的政治家，希望能解決國家的各種問題。作為反戰派，派人保護B國來的夫婿。
;薩拉丁·穆萊特
:A國左大臣，原本是北方國度來的劇團演員，獲第一王女青睞被拔擢任官，也是王女的情人。為人精明，一眼看穿納蘭巴耶爾並非真正的夫婿。
:A國右大臣，是一名祈禱師，用怪力亂神的迷信哄騙國王，與王女派的左大臣對立。身為主戰派擔心王女派與B國合作，企圖刺殺納蘭巴耶爾。
:莎拉的僕人，年輕時是王宮的理髮師。幫忙隱瞞B國送來小狗的事。
:第一王女的僕人，總是穿著只露出眼睛的罩袍，替王女刺探政治情報。
:A國最優秀的建築師，與納蘭巴耶爾合作建設水路。
;歐都尼·奧爾都
:B國族長，待人接物十分無禮，為羞辱A國沒依約讓青年和親反而送去一隻狗，打算在A國興師問罪時，說是青年半途逃跑了。
:納蘭巴耶爾的父親，是一名圖書館館長，幫忙隱瞞A國送來小貓的事。
本作中，兩個國家的生活型態和政治背景都經過精心設定。根據作者巖本奈緒的說法，A國（金之國）取材自西亞地區的國家（如伊朗和土耳其）和埃及，B國（水之國）則是以中國、蒙古、西藏和尼泊爾為藍本。
ISBN 978-4-09-138668-7
ISBN 978-957-108-234-9
抽氣循環為火箭發動機的一種開式循環。從火箭發動機主燃燒室抽取一部分熱燃氣引入渦輪驅動燃料/氧化劑泵，最后乏氣直接排出。
王后雄，湖北黃岡人，1962年6月生，中師畢業后任教小學，后取得華中師範大學學歷，1987年調入黃岡縣一中。2004年6月起任華中師範大學化學學院教授。曾主編《化學重難點手冊》等多本教輔。
杭行路站是杭州地鐵4號線二期與10號線的一個換乘車站，位于勾運路與杭行路交叉口。
杭行路站4號線、10號線均為地下島式站臺，兩者呈T形布置。其中4號線沿勾運路東西向并跨杭行路布置，10號線沿杭行路南北向并跨勾運路布置，在10號線站臺北側設有一股逆岔單渡線。總用地面積30375平方米。設置7個出入口，6組地面風井，總建筑面積36577.63平方米，其中主體建筑面積為26841.13平方米，附屬地下建筑面積為8186.5平方米，附屬地上建筑面積共1550平方米。
18區區際競技大賽
主持《東京音樂節》、
《全日本紅白歌唱大賽》
主持第17屆《東京音樂節》
〈地球大合唱〉
歡樂今宵之工業群星頌安全
〈激情〉、〈住家男人〉
歡樂今宵之七色漣漪
〈長街的一角〉、〈愛的廢墟〉、〈激情〉
1987超級新星競選
〈激情〉、跟呂方合唱
地球大合唱二十週年慈善紀念大碟製作特輯
拍擋擂臺爭霸戰〈癡情激情顯濃情〉、
〈十八相送未了緣〉
〈講多錯多〉、〈早晨〉
香港廣播60年紀念音樂會
〈You're So Vain〉、
《神奇旅程樂穿梭》〈燃點真愛〉
歌謠 Parade
歡樂今宵-友情一線牽憶蓮
〈放縱〉、〈激情〉、〈灰色〉、
〈還有〉、〈你是我的男人〉、
〈一分鐘都市一分鐘戀愛〉
香港太太競選
〈還有〉、〈你是我的男人〉
〈滴汗〉、〈一分鐘都市一分鐘戀愛〉、
〈依然〉、《鬼馬盜仙草》
管弦樂韻金曲夜
〈依然〉、〈你是我的男人〉
〈帝女花之庵遇〉
齊心同步創90 演藝同歡新里程
林憶蓮倫永亮訪問
成長'90歌曲創作比賽音樂會
〈推搪〉、〈踏上成長路〉、〈不不不〉
《香港心連心》晚會
〈前塵〉、〈踏上成長路〉
〈給我一個吻〉、〈情人的眼淚〉、
〈傾斜〉、〈還有〉、〈不不不〉
歡樂今宵 性感約會林憶蓮
〈滴汗〉、〈不不不〉、〈你令我性感〉
〈情人的眼淚〉
〈Oldies Medley〉
勁歌金曲火樹銀花紛紛 FUN
〈你令我性感〉、〈傾斜〉
〈你給我的愛不是愛〉
第十三屆十大中文金曲頒獎音樂會
〈前塵〉、〈明星〉
開心浪漫俏佳人第8集
〈瘋了〉、〈恭喜恭喜〉
オールナイトフジ All Night Fuji
第一屆亞洲鐳射卡拉OK大賽
十大健康形象頒獎典禮
〈燒〉、〈傾斜〉、〈瘋了〉、〈多謝〉
舊曲情懷演唱會
〈Smoke Gets In Your Eyes〉、
〈Changing Partners〉、
〈今天不回家〉、〈Run to Me〉 、
〈往事只能回味〉
歡樂今宵 華東水災籌款之夜
〈明月千里寄相思〉
話題人物、〈匆匆〉
〈情人的眼淚〉、〈千載不變〉
〈黛玉葬花〉
歡樂今宵胡楓60大壽
〈青青河邊草〉、〈夜來香〉
〈Jeremy〉
歡樂今宵之群星齊頌港加情
〈不捨不棄〉、〈寵愛〉
伙伴計劃燦爛笑容音樂會
〈一輩子心情〉
〈焚心以火〉、〈Greatest Love of All〉、
〈Money Money Money〉、〈野花〉
〈瘋了〉、〈沒有你還是愛你〉、
〈明天你是否依然愛我〉
PIONEER第二屆亞洲鐳射卡拉OK大賽
〈Saving All My Love For You〉、〈野花〉、
〈只怕不遇上〉
空中彩橋晚會
〈醒醒〉、〈明天會更好〉
〈舞林乾坤匯〉、〈寵愛〉
勁歌金曲之萬千寵愛林憶蓮
〈匆匆〉、〈愛上一個不回家的人〉、
〈用愛將心偷〉、〈輪流轉〉、
〈明明白白我的心〉
〈始終一天〉、〈情人的眼淚〉、
周海媚vs林憶蓮 遊戲
勁歌金曲 歌星大挑戰
〈暗示〉、〈I Have Nothing〉
打指模、名人紅星卡拉齊O.K.〈此情只待成追憶〉、捐演唱會戲服、
〈不如重新開始〉
〈愛上一個不回家的人〉、〈當愛已成往事〉
減災扶貧創明天製作特輯
〈雞同鴨講〉
〈鐵扇公主〉
SATCHI 至尊演唱會之蓮城一線勁歌 Show
〈飛躍舞臺〉、〈Crying In the Rain〉、
〈一分鐘都市一分鐘戀愛〉、〈灰色〉、
〈講多錯多〉、〈醒醒〉、〈瘋了〉、
〈我爲何讓你走〉、〈此情只待成追憶〉、
〈激情〉、〈沒有你的愛〉、
〈假如讓你吻下去〉、〈到底有誰能告訴我〉、
〈天大地大〉、〈Stand By Me〉
歡樂今宵之93 BB也瘋狂
綜藝雙星 歡樂100點
〈卡門〉、〈我要你的愛〉、
〈不必在乎我是誰〉
〈非愛不可〉、〈做蛋糕〉、〈跳舞〉
〈母親我愛你〉、〈不必在乎我是誰〉
〈從林憶蓮眼睛看個性〉、
〈相愛的時候到了〉
〈Super Star〉、〈三年〉、
〈問誰領Phone騷Quali〉、〈金鑽巨星風雲匯〉
〈包青天公審天王天后〉、
〈飛躍舞臺 Dancing Queen〉
〈多士對對碰〉
香港発エンターテインメント?シャワー
Hong Kong Entertainment Shower
〈情人的眼淚〉、〈再生戀〉、〈春雨〉、
〈天大地大〉、〈愛上一個不回家的人〉、
〈瘋了〉、〈不必在乎我是誰〉、
〈だからって (MTV)〉、
〈Hero (Acoustic Live)〉
〈林憶蓮鄭伊健出燈謎考考你〉
〈Memory〉、〈MegaMix Medley〉
全港反翻版唱片大行動
〈天大地大〉、〈天涯歌女〉、〈魂縈舊夢〉、
〈鐵塔凌雲〉、〈黑夜的豹〉、〈女人心〉
無限關懷顯愛心
〈信自己〉、〈別人的情歌〉、〈決心〉、
〈一分鐘都市一分鐘戀愛〉、〈Hero〉、〈Sing〉、
〈I Just Called To Say I Love You〉、
〈明日天涯〉、〈夜來香〉、〈歡樂今宵〉
〈Memory〉、〈卡門〉、〈玫瑰香〉
太陽計劃'94開幕音樂會
〈始終一天〉、〈多些那些〉、〈願〉、
〈Somewhere Out There〉
〈多些那些〉
叱咤樂壇演創會
〈Seven Lonely Days〉、〈給我一個吻〉
加港愛心連線大行動
〈灰色〉、〈依然〉、〈Summer Night〉、
〈說不出的快活〉、〈決心 Remix〉、
〈黛玉葬花〉、〈千載不變〉
〈說不出的快活〉、〈決心〉
超級星期天 第19集 哈林夜總會
〈不必在乎我是誰〉、〈夢醒時分〉、
〈I'll be there〉、〈整晚的音樂〉、
〈傷痕 MTV 首播〉
超級星期天 第25集 哈林夜總會
〈當愛已成往事〉、〈Summer Night〉、
〈傻瓜與野丫頭〉、〈A Whole New World〉、
〈風從哪裡來〉、〈晚風〉、
歡樂100點
北京和平演唱會
〈傷痕〉、〈祈禱〉）
《我們的愛》歡樂民生報社慶
〈I will always love you〉
超級星期天 每週一曲
〈Can't We Try〉
叱吒樂壇流行榜十周年文藝晚會
〈瘋了〉、〈每天愛你多一些〉
勁碟爆唱 Super Live 3-5
〈Let Go〉
〈一簾幽夢〉、〈楓葉情〉、
〈晴時多雲偶陣雨〉
2000年中央電視臺元宵晚會
〈至少還有你〉
Super Live 3-5
〈失蹤〉、〈不會結束的故事〉、
〈我坐在這裡〉
〈甜蜜蜜〉、〈California Dreamin'〉、
〈當愛已成往事〉
〈至少還有你〉、〈等你說愛我〉、
〈Better Man〉
〈遠走高飛〉、〈等你說愛我〉、
〈默讀傷悲〉、〈哭〉（粵）、〈不許哭〉、
〈走在大街的女子〉、〈讓我笑吧〉（粵）、
〈非愛不可〉、〈天大地大〉（粵）、
〈Summertime〉、〈Sing Sing Sing〉、
〈回到原來〉、〈不要告別〉
2001 CCTV-MTV 音樂盛典
〈花與琴的流星〉
〈紙飛機〉、〈我坐在這裡〉、〈回到原來〉
〈至少還有你〉、
〈愛上一個不回家的人〉、
〈走在大街的女子〉、〈最好的事〉
第1回日中友好歌謡祭
〈傷痕〉、〈愛上一個不回家的人〉、〈瘋了〉、
〈最好的事〉、〈至少還有你〉
第22屆中國電視金鷹獎閉幕晚會
〈有涙盡情流〉
全球華語歌曲排行榜頒獎典禮
〈傷痕〉、〈愛上一個不回家的人〉、
〈日與夜〉、〈至少還有你〉
〈快歌串燒〉、〈本色〉、〈傷痕〉、
〈Diva〉、〈不還你〉、〈天大地大〉、
娛樂百分百 林憶蓮歌唱大賽
香港國際電影節第一屆亞洲電影大獎
〈I Believe〉、〈君をのせて〉、〈追〉
〈他們都是我們的孩子〉
〈What a Wonderful World〉、
夢圓東方跨年倒計時晚會
〈灰色〉、〈不還你〉、〈傷痕〉、
〈當愛已成往事〉、
〈他們都是我們的孩子〉、
〈走在大街的女子〉、〈再見悲哀〉、
〈愛上一個不回家的人〉、〈至少還有你〉、
〈Love Will Keep Us Together〉
歡樂中國行 魅力珀萊雅 2009
〈愛上一個不回家的人〉、〈至少還有你〉
第28屆香港電影金像獎頒獎禮
〈說不出的快活〉、〈青春阿哥哥〉、
〈L-O-V-E Love〉、〈天若有情〉、
〈願〉、〈月光愛人〉、〈請跟我來〉、
北京奧運會成功舉辦一週年紀念音樂會
〈恍然如夢〉
2009-2010跨年演唱會
〈Better Man〉、〈傷痕〉、〈至少還有你〉
第19屆金雞百花電影節
〈葬心〉、〈玫瑰香〉、〈當愛已成往事〉
2010中國播音主持金話筒獎頒獎典禮
〈聽説愛情回來過〉
〈歌生.憶愛〉：〈滾滾紅塵〉、
〈遇見〉、〈盛夏光年〉
芒果群星COME芒音樂會
〈枯榮〉、〈日與夜〉
第23屆流行音樂金曲獎頒獎典禮
〈想要跟你飛〉
〈至少還有你〉、〈為你我受冷風吹〉
〈當愛已成往事〉、〈至少還有你〉、
〈鏗鏘玫瑰〉
〈寂寞擁擠〉
2013跨年演唱會
〈蓋亞〉、〈鏗鏘玫瑰〉、〈至少還有你〉
〈勁草嬌花〉
〈至少還有你〉、〈鏗鏘玫瑰〉、〈蓋亞〉
12道鋒味（第二季）第8集
巨星推薦人〈為你我受冷風吹〉
〈外面的世界更精彩〉、〈我最親愛的情人〉
2017跨年演唱會
〈為你我受冷風吹〉、〈夜太黑〉、
〈聽説愛情回來過〉、〈至少還有你〉
歡樂一家親小年夜晚會
〈為你我受冷風吹〉、〈至少還有你〉
首發歌手〈不必在乎我是誰〉、〈無賴〉、
〈Run〉、〈我最親愛的〉、〈克卜勒〉、
〈盛夏光年〉、〈藍蓮花〉、〈崇拜〉、
〈多得他〉、〈柿子〉、〈Leslie Forever〉、
〈也許明天〉、〈小情歌〉
浙江衛視年中盛典
〈蓋亞〉、〈為你我受冷風吹〉
歌手嘉賓〈至少還有你〉、〈為你我受冷風吹〉
常駐導師〈綠光〉、〈血腥愛情故事〉、
〈水星記〉、〈那些花兒〉、〈沙灘〉、
〈紅色高跟鞋〉、〈女爵〉、〈我好想你〉、
2018跨年演唱會
〈藍蓮花〉、〈不必在乎我是誰〉、
〈多得他〉、〈Leslie Forever〉
2019東方跨年盛典
〈為你我受冷風吹〉、〈聽説愛情回來過〉、
〈為你我受冷風吹〉、
〈鏗鏘玫瑰〉、〈傷痕〉
陌陌直播平臺
MOMO直播17驚喜夜
冒險之星是一個單級入軌項目提案。
單級入軌（，縮寫：）是從地面發射一個航天器直接入軌，不拋棄燃料箱、發動機或其他主要部件，屬于可重複使用發射系統的一種。目前，尚沒有從地球發射的單級入軌系統被制成，實際使用的都是一次性使用運載系統多級火箭。
理論上，使用化學能驅動的火箭發動機能實現從地球的單級入軌。但挑戰在于：軌道速度要超過、起飛階段克服地球稠密大氣層的阻力，再入階段的熱防護，綜合成本的競爭力。
在其他質量較小且沒有大氣層的天體表面發射單級入軌航天器是現實可行的，如火星、月球。阿波羅登月的登月艙、蘇聯的幾艘無人自動登月返回的月球號系列探測器等都實現了月面的單級入軌。
ROMBUS概念圖
二十世紀中葉前，對太空旅行的研究還很少。1960年代，這種工藝的一些早期概念設計開始涌現。
單級入軌最早的概念之一是工程師提出的一次性的一級軌道太空卡車（One stage Orbital Space Truck）。另也提出了一個名為“ROOST”的可重用版本。
Another early SSTO concept was a reusable launch vehicle named NEXUS which was proposed by Krafft Arnold Ehricke in the early 1960s. It was one of the largest spacecraft ever conceptualized with a diameter of over 50 metres and the capability to lift up to 2000 short tons into Earth orbit, intended for missions to further out locations in the solar system such as Mars. The North American Air Augmented VTOVL from 1963 was a similarly large craft which would have used ramjets to decrease the liftoff mass of the vehicle by removing the need for large amounts of liquid oxygen while traveling through the atmosphere.
From 1965, Robert Salked investigated various single stage to orbit winged spaceplane concepts. He proposed a vehicle which would burn hydrocarbon fuel while in the atmosphere and then switch to hydrogen fuel for increasing efficiency once in space.
Further examples of Bono's early concepts (prior to the 1990s) which were never constructed include:
*ROMBUS (Reusable Orbital Module, Booster, and Utility Shuttle), another design from Philip Bono. This was not technically single stage since it dropped some of its initial hydrogen tanks, but it came very close.
*Ithacus, an adapted ROMBUS concept which was designed to carry soldiers and military equipment to other continents via a sub-orbital trajectory.
*Pegasus, another adapted ROMBUS concept designed to carry passengers and payloads long distances in short amounts of time via space.
*SASSTO, another launch vehicle concept.
*Hyperion, yet another Philip Bono concept which used a sled to build up speed before liftoff to save on the amount of fuel which had to be lifted into the air.
Around 1985 the NASP project was intended to launch a scramjet vehicle into orbit, but funding was stopped and the project cancelled. At around the same time, the HOTOL tried to use precooled jet engine technology, but failed to show significant advantages over rocket technology.
The DC-X, short for Delta Clipper Experimental, was an uncrewed one-third scale vertical takeoff and landing demonstrator for a proposed SSTO. It is one of only a few prototype SSTO vehicles ever built. Several other prototypes were intended, including the DC-X2 (a half-scale prototype) and the DC-Y, a full-scale vehicle which would be capable of single stage insertion into orbit. Neither of these were built, but the project was taken over by NASA in 1995, and they built the DC-XA, an upgraded one-third scale prototype. This vehicle was lost when it landed with only three of its four landing pads deployed, which caused it to tip over on its side and explode. The project has not been continued since.
From 1999 to 2001 Rotary Rocket attempted to build a SSTO vehicle called the Roton. It received a large amount of media attention and a working sub-scale prototype was completed, but the design was largely impractical.
There have been various approaches to SSTO, including pure rockets that are launched and land vertically, air-breathing scramjet-powered vehicles that are launched and land horizontally, nuclear-powered vehicles, and even jet-engine-powered vehicles that can fly into orbit and return landing like an airliner, completely intact.
For rocket-powered SSTO, the main challenge is achieving a high enough mass-ratio to carry sufficient propellant to achieve orbit, plus a meaningful payload weight. One possibility is to give the rocket an initial speed with a space gun, as planned in the Quicklaunch project.
For air-breathing SSTO, the main challenge is system complexity and associated research and development costs, material science, and construction techniques necessary for surviving sustained high-speed flight within the atmosphere, ''and'' achieving a high enough mass-ratio to carry sufficient propellant to achieve orbit, plus a meaningful payload weight. Air-breathing designs typically fly at supersonic or hypersonic speeds, and usually include a rocket engine for the final burn for orbit.
Whether rocket-powered or air-breathing, a reusable vehicle must be rugged enough to survive multiple round trips into space without adding excessive weight or maintenance. In addition a reusable vehicle must be able to reenter without damage, and land safely.
While single-stage rockets were once thought to be beyond reach, advances in materials technology and construction techniques have shown them to be possible. For example, calculations show that the Titan II first stage, launched on its own, would have a 25-to-1 ratio of fuel to vehicle hardware.
It has a sufficiently efficient engine to achieve orbit, but without carrying much payload.
Hydrogen might seem the obvious fuel for SSTO vehicles. When burned with oxygen, hydrogen gives the highest specific impulse of any commonly used fuel: around 450 seconds, compared with up to 350 seconds for kerosene.
Hydrogen has the following advantages:
* Hydrogen has nearly 30% higher specific impulse (about 450 seconds vs. 350 seconds) than most dense fuels.
* Hydrogen is an excellent coolant.
* The gross mass of hydrogen stages is lower than dense-fuelled stages for the same payload.
* Hydrogen is environmentally friendly.
However, hydrogen also has these disadvantages:
* Very low density (about  of the density of kerosene) – requiring a very large tank
* Deeply cryogenic – must be stored at very low temperatures and thus needs heavy insulation
* Escapes very easily from the smallest gap
* Wide combustible range – easily ignited and burns with a dangerously invisible flame
* Tends to condense oxygen which can cause flammability problems
* Has a large coefficient of expansion for even small heat leaks.
These issues can be dealt with, but at extra cost.
While kerosene tanks can be 1% of the weight of their contents, hydrogen tanks often must weigh 10% of their contents. This is because of both the low density and the additional insulation required to minimize boiloff (a problem which does not occur with kerosene and many other fuels). The low density of hydrogen further affects the design of the rest of the vehicle: pumps and pipework need to be much larger in order to pump the fuel to the engine. The end result is the thrust/weight ratio of hydrogen-fueled engines is 30–50% lower than comparable engines using denser fuels.
This inefficiency indirectly affects gravity losses as well; the vehicle has to hold itself up on rocket power until it reaches orbit. The lower excess thrust of the hydrogen engines due to the lower thrust/weight ratio means that the vehicle must ascend more steeply, and so less thrust acts horizontally. Less horizontal thrust results in taking longer to reach orbit, and gravity losses are increased by at least . While not appearing large, the mass ratio to delta-v curve is very steep to reach orbit in a single stage, and this makes a 10% difference to the mass ratio on top of the tankage and pump savings.
The overall effect is that there is surprisingly little difference in overall performance between SSTOs that use hydrogen and those that use denser fuels, except that hydrogen vehicles may be rather more expensive to develop and buy. Careful studies have shown that some dense fuels (for example liquid propane) exceed the performance of hydrogen fuel when used in an SSTO launch vehicle by 10% for the same dry weight.
In the 1960s Philip Bono investigated single-stage, VTVL tripropellant rockets, and showed that it could improve payload size by around 30%.
Operational experience with the DC-X experimental rocket has caused a number of SSTO advocates to reconsider hydrogen as a satisfactory fuel. The late Max Hunter, while employing hydrogen fuel in the DC-X, often said that he thought the first successful orbital SSTO would more likely be fueled by propane.
Some SSTO concepts use the same engine for all altitudes, which is a problem for traditional engines with a bell-shaped nozzle. Depending on the atmospheric pressure, different bell shapes are optimal. Engines operating in the lower atmosphere have shorter bells than those designed to work in vacuum. Having a bell that is only optimal at a single altitude lowers the overall engine efficiency.
One possible solution would be to use an aerospike engine, which can be effective in a wide range of ambient pressures. In fact, a linear aerospike engine was to be used in the X-33 design.
Other solutions involve using multiple engines and other altitude adapting designs such as double-mu bells or extensible bell sections.
Still, at very high altitudes, the extremely large engine bells tend to expand the exhaust gases down to near vacuum pressures. As a result, these engine bells are counterproductive due to their excess weight. Some SSTO concepts use very high pressure engines which permit high ratios to be used from ground level. This gives good performance, negating the need for more complex solutions.
Skylon spaceplane
Some designs for SSTO attempt to use airbreathing jet engines that collect oxidizer and reaction mass from the atmosphere to reduce the take-off weight of the vehicle.
Some of the issues with this approach are:
* No known air breathing engine is capable of operating at orbital speed within the atmosphere (for example hydrogen fueled scramjets seem to have a top speed of about Mach&nbsp;17). This means that rockets must be used for the final orbital insertion.
* Rocket thrust needs the orbital mass to be as small as possible to minimize propellant weight.
* The thrust-to-weight ratio of rockets that rely on on-board oxygen increases dramatically as fuel is expended, because the oxidizer fuel tank has about 1% of the mass as the oxidizer it carries, whereas air-breathing engines traditionally have a poor thrust/weight ratio which is relatively fixed during the air-breathing ascent.
* Very high speeds in the atmosphere necessitate very heavy thermal protection systems, which makes reaching orbit even harder.
* While at lower speeds, air-breathing engines are very efficient, but the efficiency (Isp) and thrust levels of air-breathing jet engines drop considerably at high speed (above Mach 5–10 depending on the engine) and begin to approach that of rocket engines or worse.
* Lift to drag ratios of vehicles at hypersonic speeds are poor, however the effective lift to drag ratios of rocket vehicles at high g is not dissimilar.
Thus with for example scramjet designs (e.g. X-43) the mass budgets do not seem to close for orbital launch.
Similar issues occur with single-stage vehicles attempting to carry conventional jet engines to orbit—the weight of the jet engines is not compensated sufficiently by the reduction in propellant.
On the other hand, LACE-like precooled airbreathing designs such as the Skylon spaceplane (and ATREX) which transition to rocket thrust at rather lower speeds (Mach&nbsp;5.5) do seem to give, on paper at least, an improved orbital mass fraction over pure rockets (even multistage rockets) sufficiently to hold out the possibility of full reusability with better payload fraction.
It is important to note that mass fraction is an important concept in the engineering of a rocket. However, mass fraction may have little to do with the costs of a rocket, as the costs of fuel are very small when compared to the costs of the engineering program as a whole. As a result, a cheap rocket with a poor mass fraction may be able to deliver more payload to orbit with a given amount of money than a more complicated, more efficient rocket.
Many vehicles are only narrowly suborbital, so practically anything that gives a relatively small delta-v increase can be helpful, and outside assistance for a vehicle is therefore desirable.
Proposed launch assists include:
*sled launch (rail, maglev including Bantam, MagLifter, and StarTram, etc.)
*air launch or aircraft tow
*in-flight fueling
*Lofstrom launch loop/space fountains
And on-orbit resources such as:
Due to weight issues such as shielding, many nuclear propulsion systems are unable to lift their own weight, and hence are unsuitable for launching to orbit. However some designs such as the Orion project and some nuclear thermal designs do have a thrust to weight ratio in excess of&nbsp;1, enabling them to lift off. Clearly one of the main issues with nuclear propulsion would be safety, both during a launch for the passengers, but also in case of a failure during launch. No current program is attempting nuclear propulsion from Earth's surface.
Because they can be more energetic than the potential energy that chemical fuel allows for, some laser or microwave powered rocket concepts have the potential to launch vehicles into orbit, single stage. In practice, this area is not possible with current technology.
The design space constraints of SSTO vehicles were described by rocket design engineer Robert Truax:
The Tsiolkovsky rocket equation expresses the maximum change in velocity any single rocket stage can achieve:
The mass ratio of a vehicle is defined as a ratio the initial vehicle mass when fully loaded with propellants  to the final vehicle mass  after the burn:
The propellant mass fraction  of a vehicle can be expressed solely as a function of the mass ratio:
The structural coefficient  is a critical parameter in SSTO vehicle design. Structural efficiency of a vehicle is maximized as the structural coefficient approaches zero.  The structural coefficient is defined as:
Comparison of growth factor sensitivity for Single-Stage-to-Orbit (SSTO) and restricted stage Two-Stage-to-Orbit (TSTO) vehicles. Based on a LEO mission of Delta v = 9.1&nbsp;km/s and payload mass = 4500 kg for range of propellant Isp.
The overall structural mass fraction  can be expressed in terms of the structural coefficient:
An additional expression for the overall structural mass fraction can be found by noting that the payload mass fraction , propellant mass fraction and structural mass fraction sum to one:
Equating the expressions for structural mass fraction and solving for the initial vehicle mass yields:
This expression shows how the size of a SSTO vehicle is dependent on its structural efficiency. Given a mission profile  and propellant type , the size of a vehicle increases with an increasing structural coefficient. This growth factor sensitivity is shown parametrically for both SSTO and two-stage-to-orbit (TSTO) vehicles for a standard LEO mission. The curves vertically asymptote at the maximum structural coefficient limit where mission criteria can no longer be met:
In comparison to a non-optimized TSTO vehicle using restricted staging, a SSTO rocket launching an identical payload mass and using the same propellants will always require a substantially smaller structural coefficient to achieve the same delta-v. Given that current materials technology places a lower limit of approximately 0.1 on the smallest structural coefficients attainable, reusable SSTO vehicles are typically an impractical choice even when using the highest performance propellants available.
It is easier to achieve SSTO from a body with lower gravitational pull than Earth, such as the Moon or Mars. The Apollo Lunar Module ascended from the lunar surface to lunar orbit in a single stage.
A detailed study into SSTO vehicles was prepared by Chrysler Corporation's Space Division in 1970–1971 under NASA contract NAS8-26341. Their proposal (Shuttle SERV) was an enormous vehicle with more than  of payload, utilizing jet engines for (vertical) landing. While the technical problems seemed to be solvable, the USAF required a winged design that led to the Shuttle as we know it today.
The uncrewed DC-X technology demonstrator, originally developed by McDonnell Douglas for the Strategic Defense Initiative (SDI) program office, was an attempt to build a vehicle that could lead to an SSTO vehicle. The one-third-size test craft was operated and maintained by a small team of three people based out of a trailer, and the craft was once relaunched less than 24&nbsp;hours after landing. Although the test program was not without mishap (including a minor explosion), the DC-X demonstrated that the maintenance aspects of the concept were sound. That project was cancelled when it landed with three of four legs deployed, tipped over, and exploded on the fourth flight after transferring management from the Strategic Defense Initiative Organization to NASA.
The Aquarius Launch Vehicle was designed to bring bulk materials to orbit as cheaply as possible.
Current and previous SSTO projects include the Japanese Kankoh-maru project, ARCA Haas 2C, and the Indian Avatar spaceplane.
The British Government partnered with the ESA in 2010 to promote a single-stage to orbit spaceplane concept called Skylon. This design was pioneered by Reaction Engines Limited (REL), a company founded by Alan Bond after HOTOL was canceled. The Skylon spaceplane has been positively received by the British government, and the British Interplanetary Society. Following a successful propulsion system test that was audited by ESA's propulsion division in mid-2012, REL announced that it would begin a three-and-a-half-year project to develop and build a test jig of the Sabre engine to prove the engines performance across its air-breathing and rocket modes. In November 2012, it was announced that a key test of the engine precooler had been successfully completed, and that ESA had verified the precooler's design. The project's development is now allowed to advance to its next phase, which involves the construction and testing of a full-scale prototype engine.